Do you think Android fans will drop Android if Samsung made their own OS? No they would by Nexus, HTC etc.
If Samsung dropped Android they would sell 100,000 (guess) of there own OS devices and lose out on 100,000,000 devices sold.
That's how Samsung makes money from Android. Granted its not directly related to Android the end game is to sell handsets is it not?
You missed the point entirely.
If Samsung manages to sell 200 million units in the next 24 months (S4 + S5 and others) and increasingly makes more users more tied to its own software S-Apps and accessories that come with the phone or sold along with it then many of those users would choose to stick with their trusted Galaxy 'touchwiz' OS and S-Apps and accessories, than move to another handset.
Whilst indubitably some hardcore users would stick with Android, but I imagine 'hardcore' android users make up the smaller minority of general users with their S3's, S4's & S5's.....
You get your audience entrenched in your own hardware, and s-applications. You sell it to them as an invaluable tool to their lifestyle. You get them to buy lots of accessories and you keep providing new S-applications that replace / fulfil most users needs and then if you do leave android, the chances are they will move with you, as long as you can provide exactly the same experience on your own OS.
At same time, you court developers and get them to port their app to your own OS before you make the big switch, so that when you do - you already have most other app bases covered, easing concerns of those worried about leaving googles eco-system.
You ease consumers into your own way of thinking, and you sell them devices and applications that are aimed at their 'lives' .... They are already doing this with marketing for the S4.
Once you have the audience captured, and the background work/marketplace in place - you switch. The transition is barely noticeable if your touchwiz and S-apps look and act exactly as they did on android OS as they do on your own Galaxy 'tizen based' OS, and you have an eco-system in place where most of the big name apps (skype etc...) are all available.
To say users wont move because they want Android, is the same as saying users wont leave iOS, BB, Windows Phone etc.. When quite clearly as long as you have the hardware and software people want, the OS itself is less of an obstacle as you think.