Err, yours is an argument for men and women both having lower relationship satisfaction in marriage as compared to unmarried couples.
But you argument doesn't explain why married men and women have different levels, and definitely doesn't explain why men report higher levels than women.
Statistically, men and women tend to have different expectations about marriage. Thing like whose career will be the more important one, who will do child related work (all those drop offs and pick ups that take time during work day, talking with teachers etc).
If you love your job, do a lot of overtime and are happy with familly, the spouse might be increasingly unhappy without you knowing (no matter which gender is on which side).
These things matter less when you don't have children and one of you did not moved where other one has job. Meaning, they are more likely to hit married people.
So your argument is that because women can get out of a marriage easier due to lower cost, they will report lower satisfaction due to a grass-is-greener effect.
Interesting! Sounds like a theory worth exploring, definitely.
But you argument doesn't explain why married men and women have different levels, and definitely doesn't explain why men report higher levels than women.