Agreed; they tend not to be great deals for the acquiring companies long-term. But short term you can rally that team to build something else, and your likelihood of finding the mythical 10x developer (or manager) is statistically higher in a startup that successfully launched a product in a compressed time frame (even if the market didn't work out for them).

Any acquisition involves a lot of turnover. Guaranteed that this turnover is built into the models they use when evaluating acquihires. Consider how expensive most company's talent acquisition costs are though (upwards of $100k+ per candidate hired for top talent) and it starts to make sense.