Decreasing Comps at MGM Because of Wins

Are comps decreasing to the point of being almost non-existent? On my last trip to the MGM properties, I had 6 hours of play and $300 average bets, but I have received no comp offers. I did have wins on the last two trips that totaled a little more than $10,000. Does MGM not send out offers if you win even if you have decent size play? Also, it seems that express comps are earned at the rate of a few dollars per hour, which is pretty minimal for that size of play.