I dunno, vulnerability I guess? I like happy drunk girls when played for laughs too because they just kinda give up agency and go with the fun flow. It says to me, "This girl is out of it", same way as hypnosis I guess, which I obly ever really enjoyed when it was part of a seductive process or sheer, overwhelming power washing away resistance.
I mean, if I'm really honest with myself. Never really thought of it before, thanks Anon