I think this is a result of fear and marketing - if you have team leads, then you can still advertize a flat corporate structure, and startups are afraid to off

I think this is a result of fear and marketing - if you have team leads, then you can still advertize a flat corporate structure, and startups are afraid to offer the management title because it means giving up control, which is a bit crazy - you'll give up 15% of your company for 100k, but not a bit of control to a manager who is just trying to do what he can for your company.