Or why we can not trust Apple, Samsung and some others. I personally have been experienced that. Actually with every mobile device I have owned.
You upgrade your OS or apps and overtime it becomes slower and slower. This is understandable when your hardware becomes older, but I see dramatic performance drops for the same old functionalities after updates very often. As an embedded SW dev I know that It is very easy to slow down the processor wittingly. Do they make it...can't know for sure.
The bad thing is - if you don't upgrade your system some apps stop working or become buggy, maybe because the servers use some new features that are not supported by your old SW, that's normal.
So you have no choice. Well, somebody have to buy the new devices after all, right :D
Maybe I'm biased, I don't know.
I recommend you to watch the video by Dave Cullen and please share with me your opinion on this topic.