I chose the same. I find harems who only show interest in the MC a bit boring. Having everyone involved with everyone makes it feel like an actual relationship between the characters, and not just power fantasy.
Also, can you imagine Lydia not it getting on with the other girls in an orgy? That girl is equal opportunity thirsty. It would require rewriting her character.
I agree, to some extent. Having them run off and have fun without the MC *occasionally* is sometimes fun, but mostly only when it's when the MC is busy with someone else in the harem. i.e. "Ooh, that looks fun, I think I'll join!", or "The (MC) seems busy, but I'm horny as hell... who else is home?".
At the risk of mentioning another game here, I'll just drop that Sisterly Lust had that same vibe - the MC got together with the girls both solo, and in groups, and frequently one of the harem girls would simply join right in, which made it that much hotter. And they sometimes got with each other when the MC was busy elsewhere. Basically an "all you can eat buffet, but just for those in the harem, never forgetting to involve the MC where possible".
I like where Elmwood U. is going so far, just trying to stay patient for more content, and would love to see it mirror this kind of setting and have the girls be open to almost anything, knowing they're in a harem.