The thing about city breaks is they tend to be to places that can also attract business travellers.
But the timetabling doesn't suit either. A pattern like -Tu-TH-Sa- isn't going to get many of either category on board.
Bafflingly, EI use their aircraft on a Monday morning to fly to Faro and Malaga.
In general, business travellers like to fly Monday and Tuesday morning and Thursday and Friday evening. And those are also timings that can suit people taking a weekend away.
Passengers to sun destinations don't tend to care so much if they leave in the morning or afternoon.