Question about MGM Players Club Ratings for table play?

Hi... I was just out in Vegas with some friends. I gambled pretty regularly with two people; we all have Players Club cards and used them religiously at the tables. My two friends are married and on a linked account (2 card numbers that go back to one Players Club account) and I am solo on my account. The husband gambled about as much as I did-- consistently $20 + odds on craps plus assorted line/hardway/feild bets, and the wife bet about half of that. During the play we got equal comps (cigarettes, etc). At checkout, their food tabs had been comped and one night of my room had been comped (separate bills, separate rooms) so I got about $75 more than they did in freebies. Now that I get home, I am getting tons of emails from the MGM casino family offering me a casino host for the next trip and Players rates but they are not getting anything.

My Q: why am I getting more comps when one of them gambled as much as I did and between them, they spent more?

(No I am not complaining!)