Makes good business sense
I would never call such horrifically predatory tactics “good business sense.” It’s abuse of market position and should draw the ire of antitrust regulators, as well as make their product a major business risk for any new projects.
Let’s not forget that Unity recently merged with a malware company, so borderline-illegal predation is their entire business strategy.
Because they realize that a huge number of their customers are small indies, and they want to be able to squeeze them - the majority of their customer base - not just the minority of big companies (who are also the most likely to fight back legally).
Just look at how their scheme squeezes smaller, poorer developers way more than big ones. If Unity went by points like, say Epic does with Unreal, they could shake down the big developers… but wouldn’t get much out of the indies.