BHX as a base was "launched" with a NEO, It's likely just down to how it fits into the aircraft maintenance cycles in the long term rather than anything to do with aircraft going tech in the short term, all aircraft are susceptable to faults and failures and there is probably an argument to be made that if anything the CEO's are more vulnerable to that purely through age.
EZY are as savvy as its yellow and blue competitors. If you ever notice a frame swap they've performed, it's generally not a positioning flight unless they absolutely have to. A crewed flying airliner without paying passengers is a huge cost drain (Unless you're TUI lol, they seem to have stuff moving around empty all the time). What they tend to do is swap two aircraft from different bases landing at the same destination at similar times, for example, the two aircraft may operate BHX-CDG-LTN and LTN-CDG-BHX, with Luton having a large EZY maintenance presence for heavy checks and overhauls etc.
To that point, I think it's luck of the draw and we'll see NEOs in the future.
I'd love to see BHX be considered to have enough 'high-density' routes for EZY to base a 321 at BHX, that'd definitely be a NEO.