Well, it's quite brutal in that way.

I kind of see it like "the more you interact in the Ecency ecosystem, the more likely Ecency will support you".
Besides, the boost is not a granted vote. On average, about 50% of boosted post are really then voted.
Promotion is just a way to spread more the post in Ecency (not Hive), to get more visibility. And they can be both purchased with points accumulated with comments, votes, posting, delegating, referring users and more