If memory serves me right, Boeing destroyed all the tooling for the 757 line, thus making it almost impossible and very costly to restart it. Besides "hypothetically" it would hurt future sales of the 737. Why order an old airplane with 70s and 80s tech when you would want a 757-200/300NG?

Sad thing in the late 90s Boeing was begging NWA, Delta and anyone else that would listen to order more 75s or they would shut the line for good. It's not like the put all the tooling in the desert for storage. Then when gas prices went up, the 757 really showed how well it could do. I bet the 753 would be still selling if it was open. But it's all a pipe dream, the 757 line will never be reopened. Would hurt the 737 (-900)max orders too much.