I think this is all related to the "economy" of Steemit. Payments to authors are due to new buyers of tokens, buyers are attracted to the possibility of obtaining additional income from renting SP. In fact, many people just need passive income, and they buy tokens for POS-mining. Available to all boosters is the least evil here. Without redistribution of emission to investors, the entire pyramid will quickly collapse.

This is the true explanation for boosters. Almost no one actually wants to pay authors out of their own pocket for their posts.

p.s. I heard that in new forks of Steem the distribution of emission is 90/10 in favor of investors (curators). With such distribution, you can probably do successful project without boosters. But with boosters the percentage of shares in distribution is regulated by the market, this is correct I think.