Hello Whitesnake29,
The answer to your question, to make money.
With each update, your device gets a bit older, while still improving some things, unless an uproar is made, it’s just not cost effective for them to fix all bugs 🐜. They need a large percentage of the population to complain, I have no idea what the percentage is, but they have a number they go by. Also, if the problem is made public, or they’re being sued, they address that issue because their brand reputation is affected.
Otherwise, most software updates little by little fix minor bugs they may find, and improve the bells and whistles in their apps........however, still aging your device until it will not update any more. Thus my First Generation iPad, my Samsung S4, S5, and slowly my current S7, have either ceased to work or can no longer accept updates.
There are places that know how to “refurbish” some devices, but what you pay for that, it’s a personal decision that you’d have to determine if it’s worth it for you.
This is what keeps them in business. Sadly, I’ll need a new phone soon, maybe within a year, I’m sure.
Hope this answered your question.
Ali