Earlier quoted context omitted.
Even today I see an increasing number of friends moving from 2 years cycles to 3 year cycles. The "killer app" for smartphone refresh rates staying low are (1) battery degradation and (2) forced OS updates for app updates, which in turn slows the phone down to compel an update[1]. [1] I'm actually curious if OS updates slow down older phones these days. This was the case 5 years ago but perhaps things have changed/
I have an iPhone 6S - I'd say OS updates do slow the phone down, but they also tend to be really buggy and generally rubbish for a while. I think it's probably more bad engineering and software quality than anything nefarious.
[1] http://money.cnn.com/2017/12/21/technology/apple-slows-down-...