Lack of large funding, like maybe above 100 billion dollars or even more? Plus, the amount of public data needed to train. It's a lot of work, and then there's the question of whether it will be worth it. There's always speculation that maybe the project needs to shut down midway, and all the money and energy would just be wasted. That's why even big techs work like a small startup on these.

Maybe this video is part of the problem