No outsourced airplane can fly for Delta that is configured with more than 76 seats. If it has 77 seats installed, it has to be flown by mainline pilots.

Delta has opted for a 2 class product, and has even pulled seats out of aircraft that used to seat 70 in order to put in a few first class seats.

There is also a maximum gross weight limit on top of all that which is 86,000 lbs (sickening, I know)...but that restricts the bigger Embraers from operating at their full capability.

Perhaps if you sardine can people on board, sure you can fit 90 people on board a CRJ-900... but that is not an option, nor does Delta want that in their product.... and if they did decide to sardine can 90 people on board, you'd find us double breasted van admirals driving it.