investors dry up, prompted by a scandal (or not)

or someone figures out how to do AI at 1/100000th the CPU/memory on the edge

a company or two collapses

all the other companies now back way off

now the bubble is popped

AI returns 5-15 year later

The bubble will pop if/when credit markets stop providing new money. They would do that if they just run out of money to lend or they decide that AGI is impossible.