Riding w others on track, especially random people only grouped by some arbitrary speed grouping, requires attentiveness and quick decision making along with a good amount of trust. When approaching a slower rider, size them up real fast. Pay attention to where their line is, notice where and how hard they brake, and watch where and how hard they get on the gas. Based on all that, make a decision about how much u trust them and their skills. Do u trust them enough to pull up close and pass them around the outside? Or do they look sketchy and will require a lot of space? Not everyone deserves the same level of trust. But it's pretty ez to spot the sketchy ones and the skilled ones in a very short time while on track. if/when everyone does this on track, even the people passing u will do the same.
Aside from all that, not enough ppl at track days take advantage of this really ez way to get unstuck from a big group. others have already said it. A few corners before the end of the lap, throw a hand up. Then before pit in, get off the line... Then slow down and exit the track. Roll through the hot pit at 50mph and re enter the track safely. If u were matching the speed of the group before, u won't catch them in the 3-5 laps u have left.