Years ago when the modern reality TV was just getting started I remember the shows having normal average people in them. Sure, some of those become "stars" later just by being on those shows. But nowadays it seems that all the shows are full of people already famous from something else.
Maybe it's different in the bigger markets, but here in Finland we don't really have many of those really big stars. And even they aren't anywhere close to those filthy rich and famous people like the Hollywood stars.
Being a little bit famous in Finland isn't that hard, so basically the "stars" in those reality shows are still pretty normal people. Being a media person is just a job among others. A job that might make your name known to a bit larger audience than the normal day to day jobs. It might open you some new opportunities, but it also brings your fame along. Some of that fame might not be to your advantage.
In the end, even if you were an average person nobody knew before, just being on one of those reality shows would already make you an average "star" in here. So even if they would be nobodies before, the shows would end up being full of average celebrities. Also, for an average person like me who doesn't really follow such people most of the participants are unknown to me anyway (at best I might know somebody from another reality show). So there is no difference.