I personally have zero interest in playing beta. I wouldn't care to waste the time I have available to play when I could spend it further progressing my actual character.

As for why they wont give legacy players priority I suspect it's because they want to advertise the games to potential new players via beta keys. It's a pretty common marketing strategy so don't get your hopes up.

Look on the bright side though, all the time you would have wasted playing beta you can spend actually doing something productive towards the progression of a character you will actually use.