yes, loyalty just reduces the cost per click, but the math is the same, so they buy 100 people instead of 10 people with one reservation, but the game is the same.

EDIT: also think about how many times people book per year, maybe 4-5 times in the upper quantiles? so if booking pays 3$ for you, it will take a couple of months until your next booking so they can reinvest your 15% commission to buy other people.