Every single phone shipping with Qualcomm SoCs are at the mercy of Qualcomm. When they want you to buy a new chip, they'll kill support for your current chip, meaning that the manufacturer will have to spend effort making newer Android work with older kernel versions if even possible.

My Sony Xperia Z3 had software support killed by Qualcomm. They refused to provide the binary blobs required to make next Android version work despite the CPU being perfectly capable, as evidenced by the beta builds that only needed a small update from Qualcomm.