Earlier quoted context omitted.
If new startups agreed that they wouldn't leave their users out to dry if they got acquired would you be more likely to trust them and use their service?
No, because how would they enforce that? If your company is acquired, all that goes out the window anyway.
In a sense the promise is a "non-credible threat" in game-theoretic terms. It would attract users if they carried it out, but because acquisition happens after the user-attraction stage they don't have an incentive to carry it out. This means they won't rationally carry it out, which means they don't attract rational users. This situation can be avoided if they "tie their own hands".