I can't speak for the instructors at Alteon, but I can give you a general overview of sim instructors.
I have found that they fall into 4 broad categories:
Retired Airline pilots
Unable to fly: Lost medical/divorce with children/other family issues
Furloughed pilots
Professional sim jockeys
Some miss flying, some are waiting to get back in the cockpit and others are just passing time. I see some of each from each of the 4 groups.