Masha is a nymphomaniac so she is horny all the time. Nelly can get ridiculously horny having sex 3 times in an hour, something impossible for Masha because she wouldn't have finished the first one . After The Goddess has bated it seems for a long time afterwards she can't think of anything but her kitty. As far as we know from very good sources there is no bonus for sex in the couples's apartments so this is just natural horniness. Yes there might be other incentives for Barcelona girls but why can't they be like those 3? Bea seemed to lose all control when she got horny.
Yes I am sure some of it is put on but the plain reality is girls get horny and they have as much erectile tissue as a man and when you get erect how rationally are you thinking?