[throwaw-zxcvbn]

It's not only how strictly you keep tabs on things, the nature of the exchanged "goods" changes as well, in particular it becomes more asymmetric.

In an equal relationship, both contribute economic resources, emotional support, domestic work, sexual pleasure, etc. Traditionally, in the West, there was an asymmetry in that the woman provided the domestic work, the man the outside work with the concomitant salary; but the asymmetry has shrunk over the decades, due also to the increased opportunities of women in the work force.

In these sugar relationships, there is massive asymmetry in the nature of the contributions; it's an intermediary between prostitution (pure money vs sex, short term) and marriage (lots and lots of stuff vs lots and lots of stuff, long term), but arguably closer to the former.