I'm a marathoner (I don't compete in triathlons) but I just googled transition area and it means what I thought it means, having been a spectator at triathlons. But yes, IF I were a competitor in a triathlon, I think I'd be annoyed at people without race bibs in that area. Lots of traffic and some athletes fatigued and hard-at the task at hand. Probably not a good mix. I've run Boston though, where some bandits do get in, but I'm not sure if a bandit could compete in a Tri without getting busted. Bike on standby, etc. So people in the transition area without a bib are probably just clogging things up.