First, they did reward players for leveling on the test server. In a title reward and by being able to see the content earlier.
Second, your evidence is anecdotal, what if I said that I knew 2 level 50s who fill out bug reports all the time, and are active members of the community who discuss class balance, PvE and PvP content on here and on the SWTOR subreddit? My point is, just because 1 person at level 50 doesn't help the game, doesn't mean that ALL of them don't.