Yeah, that’s the core issue for the US carriers. Ordinarily, a stretch version is cheaper per seat mile, but that changes a lot when you go from being the largest (and best plane) that can fly with two cheap regional pilots to the smallest that can fly with two expensive mainline pilots. That’s why there are precious few sub-130 (or even sub-150) seat mainline aircraft; airlines and unions haven’t had much success coming to an agreement that would put more of them in the fleet.

I think there is also less in common between the E190/195 and the E170/175 than on most stretches, which has harmed sales elsewhere where they might both be in one airline’s fleet. I think Virgin Australia was very unhappy with the E190’s reliability. All perfectly understandable reasons why airlines don’t love the plane as much as passengers.