Why can’t reporting structure be more flat?

I work in one of biggest bulge bracket (think one of BofA Securities or JPM).

Our reporting structure used to be more flat but now there is new initiative to add more managers. 
I used to report directly to Managing Directors but now I am reporting to a director with other two VPs.

My new manager doesn’t have any actual work so he try to make my work harder to be done as he is keep giving me unprofessional and immature tasks. 
I also lost a lot of more visibility.

Why banks suddenly want to adding more managers and making reporting structure less flat. Doesn’t it increase the cost to them? Most of middle level managers don’t have actual work to do and totally unnecessary. What’s the point have so many managers?