One theory is that hunting and gathering stopped because the human population exceeded what could be supported by mega fauna, and early peoples had no choice but to settle down and defend what resources they could gather.

It likely started with semi permanent settlements, simple fortifications that could be returned to year over year, and when it became too difficult to leave again, or when they found themselves unable to return to a location they were expecting to, they settled down permanently.

But you really can't go out and hunt when you can't leave. So they started to depend on agriculture, and what livestock they'd been able to keep with them.