@Sevanw has a point though. The removable battery and SD card is on its way out in general so i'm not sure why that's being brought up. With the materials that Apple uses on the iphone (compared to the S6/Note5) they get away with murder with what they charge. People still buy it in droves because they make a great product.
People also buy Apple because it's the only maker of IOS devices. You literally have no choice if you want a new iOS device but to buy an iPhone. That puts Apple in a very unique position. One Samsung fails to understand.
However by far the main issue is :-
Cultural differences - buying habits (Android/iOS)
If we look at software buying habits once devices are purchased we see a similar pattern emerging regarding users - iOS users DO buy more paid apps than Android users - it does show more of a willingness to pay for what they perceive as quality or value, whereas Android users tend to go for more freemium ad based software, looking for the best free deal and not really too fussed about the compromise i.e. advertising. In many cases developers simply don't have a paid for version of the software on Android compared to their iOS version because they know there is an expectation and general unwillingness for Android customers to pay / purchase. Heck you should look at Nova Launchers blog sometime - despite being 'THE' de facto alternative launcher and one of the most used launchers for Android users - less than 15% of its users have actually paid the $2 for Nova Prime. It's indicative of the average Android user - willing to trade off features / extras for even the most nominal of price savings.
Android users have traditionally always been looking for the 'better deal', they tend to traditionally want more bang for their buck and are not willing to pay over and above the competition. They see Apple's pricing as the line in the sand that they don't / won't want to cross (and for many if they are going to cross it - well they "may as well have an iPhone" kind of thought process).
It's why we see such hype and demand for cheaper OEM's like OnePlus - it's all based on value - the trade-offs in a cheaper device are irrelevant for the most part - it's the cost that is the defining factor for android devices and this is why Samsung has slowly found itself in a bit of a pickle.
By slowly creeping up-to and in some cases above Apple's pricing model, its crossed that line which for many Android users is a line too far. The issue isn't what Apple are charging, it's the myriad of other competitive android OEM's who are charging significantly less. Do they have all the bells and whistles of the latest Samsung flagship? Maybe not but as the 'freemium culture' shows in the android space - android customers are willing to make a trade off for what they perceive as significant $$ savings in their pocket.
Samsung makes great hardware but it's competing not with Apple - it's competing with every other Android OEM and moreover it's competing with the 'culture' of the traditional android buyer. One that has traditionally been unwilling to pay out as much as iOS devices owners.
Samsung's waning flagship sales and depreciating yearly profits should be an indication that their strategy of pricing high and going after the iPhone is not working in the West, and exacerbated by their low-mid range devices still overpriced and not competing in developing markets like China, India and African subcontinent. .
There's a plethora of eager OEMs willing to steal the price conscious Android user at every turn.
Likewise Samsung used to at least define itself different from Apple by having features such as SD Card & Removable batteries. It continuously played on those strengths through years of very heavy PR & marketing campaigns. With those gone and prices ever increasing to and above Apple it's no wonder why some Samsung users who may have previously always chosen Samsung over Apple may then decide that if those things are no longer a factor / differentiators and pricing is similar - to bite the bullet and go iPhone if they are going to be spending that kind of money.
Likewise the waning sales are also indicative that just as many of its traditional android base are turning away and now looking elsewhere for better bang for buck.
Android users are not as brand loyal. They will shop around, and they can. There is so much choice of alternatives. I equally have no doubt iOS users would be less loyal if Apple allowed other OEMs to use its OS.
This is not about devices being better or worse than each other. It's a 'counter' culture thing more than anything else and it's one Samsung is failing to understand itself.
There is always room / audience for an android OEM to offer the 'highest end' device at higher pricing ... sadly for Samsung it's not and never will be the same volume as Apple because of the historical Android consumer counter culture and the constant competitiveness of its other OEMs.
--- supplemental (forgot to say)
Likewise if Samsung want or expect it's customer base to pay the premium for a 'premium' product - then there has to be some serious changes to its software policies. Touchwiz must be re-engineered so it's not a bloated hog / resource killer. This is not a google services issue, as other OEMs run all Googles android services without their software overlay consuming as much resources as Samsung's, despite packing most of the same extras. Likewise and importantly they need to offer the same level of updates and future support that iOS devices owners are used to if they are going to charge the same premium price.
We should be getting new android updates and more importantly the newer Touchwiz iterations every time they are introduced for at least 3 years of our flagship device. Not stuck with older versions of Touchwiz on devices less than 6 months old. Likewise updates generally and their rollout needs to be radically overhauled for their premium line. Users should not be waiting months for an update and as soon as it's available it should be rolled out globally. It's what we as consumers should expect as a premium support for any devices holding a premium price point.
Expecting Android users to pay a premium and still make compromises whether it's hardware or in this case software will just further drive some Android users into the arms of other OEM's and some in the direction of Apple.