Well, hypothetically, if they do, then they just buy the `.com` and wait for the Startup/Company to become popular and sell it to them or their competitor(s). So far, any succeeding company beyond a certain clip, always buys the `.com` at a price, eventually.
I wish companies would stop doing that. Zoom(.us) shouldn't have bought zoom.com and Notion(.so) shouldn't have bought notion.com. Not only could they have saved a few million bucks for themselves (& by extension their users) on something which even to this day serves no purpose no other than redirection, but they could also have helped set precedents, reducing pressure on future companies to acquire .com domains.