I think it is the feel on getting on the single aisle plane that makes the 757 BF experience less desirable. Other items in my view:
1. Expectation that BF should be widebody
2. No standing areas in 757 - feeling of less overall roominess.
3. The galley is right there in front of you, with the service light on during service. No FA behind the curtain like a widebody preparing the food.
4. My experience - 1 FA preping the food and 1 doing the service. Gives the feel of domestic service on a 753.
5. Lower ceiling.

Overall the 757 just does not convey the same luxury travel experience - and again this is my view only.