It's not like Apple products fare much better on the deprecation front, although for different reasons.

No, not linux itself though, rather it is the phone manufacturer who do not want open their kernel source code so that random developer can reuse their phone even when outside support terms.

This is typically an issue with the manufacturer of the System on Chip, such as Qualcomm, Mediatek or Broadcom.

They’ve likely done some CBA and determined that porting their existing platforms to new operating systems requires a lot of work, and it’s far easier to sell a new SOC to OEM instead!

TLDR; blame Board manufacturers and not the Linux operating system/community as a whole. Although Google is trying so very hard to decouple the Operating system from the drivers as a whole.