Jet2 don't need the extra range that the B757 has, which is why they went with the B737-800 for a mid size aircraft and the A321 for a slightly bigger uplift.
The A321 is far cheaper to operate than the B757 with only a fewer seats than the B757, which is why Monarch Airlines retired the B757.
The RR engines on the B757 are getting harder to get slots for any rework required, this due to the amount of Trent 1000 work being performed by RR and other approved RR repair shops.