This is planned obsolescence at its worst .. :/
(At this point, Android management seem to be thinking "What are the other alternatives, Windows 10 Mobile .. haar, haar ..")
This is more a cavalier attitude on the part of Qualcomm who do not support their own hardware for a reasonable length of time, and who do not foster open-source driver development which would at least allow the community to bring new features to older hardware in some cases (Vulkan being the prime example).
Now they are tightening it up a bit which as a developer I support but honestly end users are being screwed, and the root cause is Google not Qualcomm in my opinion. Google could have from the start been stricter about certification if they really cared about delivering a good experience to end users and developers, rather than just sending out a shitty product quickly.
Imagine Microsoft blocked Windows 10 (or any of the next builds) from all the GPUs who don't support DirectX 12, so that the developers can write DX12 software more conveniently.
This obsolescence of multiple hundred $€Ł mobile devices inside 18 months is getting silly.
Your frustration is misdirected. The CTS and Google Play Services are the only tools at Google's disposal for inducing market changes. Perhaps manufacturers will demand longer support periods for upstream hardware, for instance.