Sure they did. They just didn't care to enter. Kinda like my protag in Gen V. --- There is more than just Good and Evil, Light and Dark, Black and White. There's a myriad of colors that you won't see if you look at the world in two extremes.
I guess at least 1 protag per set of games is officially a Champion, just that since G/S was intended to be a continuation of Pokemon R/B/Y (and was called Pokemon 2 in development) only Red was actually mentioned by name and fought personally.
Generations 3, 4 and 5 has a problem with Schrodinger Characters, mostly due to Genders and who is the "main" Protagonist, doesn't bar the fact that linking up with the memories doesn't do anything, which is a shame, but again, it was probably done like that as to avoid the player from making a bad team in B/W then transferring THAT team into the PWT, making that match an anticlimactic battle.
Weirdly, if the BW Protag was a challenger in the PWT, there would've been 8 Champions to fight, rather than 7...there was even unused text in game for Hilda and Herbert. --- RSN: Plucky9, Total: 2402. KoL: Plucky, currently a Pastamancer ACNL/3DS FC: 4897-5920-6758 Ricky of Farm
They chose to stay at the Pokemon Leagues of their respective regions, letting Lance, Cynthia, etc. compete in the league. --- "Murder of the living is tragic, but murder of the idea is unforgivable." - Janus, speaker of the synod