Hi
The pb is that the B757 has become uneconomical burning more fuel than the A321 with only marginaly few more pax.
When it comes to other operators B757, 2 facts needs to be looked into. The number of doors for high capacity config and the reinforced floor to accommodate 235 pax versus 190 for scheduled legacy airlines. So they maybe lots of A/C arrond but not suitable....And why does Delta have B757 available afterall.....