Many people say it's because pool has a dark and dirty public image due to gambling. But that's bs.
It is the common image though.
Whether that's true or correct doesn't really matter in an age where people scream out their thoughts as if the volume makes it more factual. If they hear something they don't like, they will find a random internet quote that backs up whatever inane things they come up with and then it becomes true for them. That or they come up with a quotable name for it like yelling out, "fake news", or, "libtard", even when it doesn't fit. There was a time not so long ago people made it to the moon with slide rulers. Today we have to remind people what turn signals are for.
Pool is losing ground, but only in North America. It's alive and well in most other places.