As a crew member, we are not assigned a "route", nor do we bid on a "route". We bid each month for a "line of flying" which is made up of different "pairings" or "sequences". A pairing or sequence is a group of flights that make one "trip". I may, for instance, have a 3 day pairing. That means it's a 3 day trip. Which means I am gone away from home for two nights/three days. A line of flying is made up of various pairings to make up a schedule for the month. While there are lines of flying that comprise the same flights on the same days, in order to be efficient, many times the crew planners mix things up a little bit. I may do a "turn" (just an out and back trip) to Burbank on one day, and a Sacramento turn the next day.

Most crew members like a clean line, which is to say, they like to do the same things on the same days for the entire month. As the airlines grow, it get's harder for them to do that. So - that is why you don't see the same people on every flight. With schedules changing every month, and the days of a Flight Attendant being assigned a "route" gone the way of "stewardesses" - you won't often see the same crew members.