Is there any particular reason for the repetition draw instead of just offering a draw?
The idea is to try and provoke games happening, even if the players come to the table wanting a draw (someone can still botch their opening!). Ultimately though, if GMs want a draw, they'll get it.
This is somewhat pedantic, but 3-fold repetition is not automatically a draw (at least not according to FIDE rules). A 3-fold repetition allows either player to claim a draw, but it doesn't allow an arbiter to declare a draw if neither player claims it. Only a 5-fold repetition allows someone other than the players to declare a draw.