Yes. I was wondering the same too. Did it have to go there? But apparently it did.I know what you mean, and it's hard to explain. Their bond seemed too deep for sexual interaction? I don't know, it just didn't need to go there, I guess. However, Elisa was a pretty regimented, dedicated sexual being!! LOL
Guillermo said in an interview he was very purposeful in demonstrating early on exactly what "dedicated (and "regimented", lol) sexual being" Eliza was. He wanted to distance his movie right from the start from the innocence of the Disney version of Beauty and the Beast, but also he was just as purposefully not going into anything kinky either. He wanted the sexual component of their relationship to be just a natural extension of their love.
I completely get what he wanted to do, and I'm totally on board with it mentally. I just didn't feel it. Especially after the mechanics of it were presented in such a comical manner. It was just funny, like it was for Zelda, that ok, they are actually "doing it", and perfectly acceptable, but for me nothing sensual seemed to transpire, even though their physical interactions were all deeply loving and filled with wonder. But after the water was drained from that bathroom, she certainly looked awfully pleased.