There are multiple options:
- best flight times for the route flown
- best price in C
- EK being the only airline flying to the specific destination city
- personal preference (could be)
- better quality in C than other airlines
- availability
If middle-seat in C is not ideal for single pax, for families this is a very good option. Also, very good option for upgraded pax, I'd always give up any seat in Y for a middle-seat in C
