Plenty of answers to similar (but I would say not quite the same) questions deal with issues of cost - cost of ejection seats, lower payload capacity due to weight of ejection seats, cost of checking seats and parachutes on a regular basis, etc.
But there is another key issue: How useful would they be?
There is a big difference between military and civilian flying: war. Ejection seats are used in several different scenarios:
- Damage due to war - missiles, guns, being chased "out of the sky". These things, hopefully, are extremely rare for civilian aircraft compared to military aircraft.
- Test flights. Military aircraft are the ones that (generally speaking) push the limits on speed, altitude, etc. Plenty of pilots have ejected from military test flights.
- Carrier landings. Scary when they work. Potentially fatal when they don't. A few feet off on land and you crash into grass before the runway or after the runway and have a chance to survive. A few feet off on a carrier and you are in the water and ejection is often the only realistic way to survive.
- Air tanker refueling. Just one example of a dangerous activity routinely done by military aircraft and not by civilian aircraft where an accident can be deadly and ejection seats key to survival.
While most military flights are really just practice for war and not the real thing, the maneuvering involved and speed (except for the Concorde) are often quite different from civilian flights.
The end result is that the use case for ejection seats - the situations where it would be useful - is simply not the same for civilian aircraft.