Most Android makers give up on support no later than the end of production of the hardware.
This, and all this.
This is because SoC vendors (ahem, Qualcomm) don't bother updating their proprietary drivers across Android version changes.
OEMs use them as a (perfectly valid) excuse to their greed.
Well, it's better than SoC "vendors" who don't bother releasing drivers (ahem, MediaTek).
So we gotta improvise.