Neovim's goal is remove cruft and shrink the codebase. Adding a terminal emulator, a completely orthogonal feature that makes no sense in a text editor to begin with, is contrary to this goal. They wasted time and worked on the wrong thing.
Vim already allows you to use :shell. Neovim took it a step further with the added benefit that you can treat the output as buffer text. Just because you can't see the advantages this gives developers doesn't mean it was a waste of time.
:shell is completely different. That's vim stepping out of the way while you run a subprocess. Moreover, vim having it is not an argument for Neovim to have it. If vim really had a terminal emulator Neovim should have removed it.
