No, to prevent serious battery degradation due to overuse from changes in iOS, allegedly. And as if that's an excuse - if that was the real issue, they could have provided it as an option.
If a new update slows down your phone on purpose, for whatever reason, and hides that from you, people understandably might avoid new updates.
This part from the first paragraph is important for you to understand:
> slowed down the performance of older iPhones in order to stop them shutting down without warning
This didn’t affect someone whose phone was working perfectly. It changed it so your phone got slow instead of crashing.
The reason some people held off on updates was that a bunch of confidently wrong people went around saying this was planned obsolescence and never went back to apologize for giving false advice.
The battery was already shutting down when the processor was being overworked as the battery degraded. This is physics. The update tried to alleviate that. Would you rather your phone shut down or slow down?
If a new update slows down your phone on purpose, for whatever reason, and hides that from you, people understandably might avoid new updates.