No offense, but you guys are having a problem where you're saying, "It doesn't make sense because MC doesn't get anything out of that.". But you're speaking for your *personal* kinks. The MC is a self-insert. Personally, I can 100% say I would get something out of Laura freely sleeping around. I think it's hot, sue me.
It's not about her "hiding it", it's about it being so normal and casual to her that she doesn't feel the need to explicitly tell you about every encounter. Would she tell you if you explicitly asked her? Sure, but otherwise it'd be like her telling you what she ate for lunch. Maybe it was noteworthy enough for her, she does, but maybe not if you don't ask.