If you take a look at the ios device support charts you can see that the trend is that every iphone gets 1 year more support than the device before it. My 2014 ipad is getting the upcoming update while 2 year old android devices get cut off and budget models never get updates.
I got this 2014 ipad second hand recently and it works more than well enough. I expect this is a big reason for a drop in sales.