I used to love upgrading back during the 2G/3GS era, because there was always an improved feature or something. The iPhone 4 had the Retina display for the first time, the iPhone 4S had Siri, iOS 6 had Siri on iPad, Snow Leopard looked AWESOME compared to what came before it, and so on.
Even the Android side had some rather interesting phones, slider phones, smart flip phones, folding tablets, etc.
But then iOS 7 and up happened and since then everything has been meh, boring, all flat glass slabs, sliders are extinct, etc. UI design is STILL ugly to an extent. Apple is bringing back some subtle hints at skeuo but I will never 'get used to flat design'. Can't wait for skeuomorphism to return and give me a reason to upgrade again. There's just nothing new I need or look forward to. Smartphones, tablets have stagnated and new models are no longer interesting enough to warrant an upgrade these days. The only real changes are removing features I still use--headphone jacks, home buttons, etc.
I just miss the massive WOW that came when the first iPhone was launched amidst a sea of convoluted 'smartphones' ala Palm Treo, BlackBerry Pearls, and Moto ROKRs. Where's that WOW factor today? Three cameras? really? HTC did multiple cameras with the M8 and we all know what a flop-a-rooni that was.