Because we have spent a lot of time and money using AI to generate code and have been unimpressed with the results.
As for why they got accepted so quickly 1) the industry's long running desperation to deskill computer programming 2) the addictive psychology baked into LLMs "That's an elegant solution! Shall I ... ?"
Also, a bucket for VC to put all that NFT, IoT, blockchain, VR investment into. VCs gonna VC and the last 15 years of bets failed so the last few years have been a transition away from those toward "the next thing".