You are absolutely right. POC is always a great option but there are frequent challenges of vendor rushing, a later change in requirements, or insufficient Eng resources to check every box (we'll typically rely on the word of sales team in that case).

Vendor selections can definitely always be better, but there doesn't seem to be too much flexibility for buyers when all said and done. At bigger companies annual commits (or longer) are welcome, but we've certainly had tool that are a total failure yet we're stuck with the bill. Someone on the buy side ends up seeing blame too, even if not our faults i.e. missing key feature that was misunderstood in buying process