It's the exact opposite, the girls are too used to seeing it by this point, heck some of the rewards that have been done are exactly to please his D, haven't you seen his D getting sandwitched between Kyouka and Tenka's butts in the bath before?
Tenka specifically have been intentionally stripping his boxers off multiple times with her eyes directly looking at his D.
Everyone by this point know that the rewards is always sexually related because that's simply what both "Yuuki" and the "Lender" "wants", but won't directly admit so they are just openly doing it. It's only when he's being lent to underage girls like Nei that the rewards aren't explicit, obviously because he ain't a lolicon.
The more you use Yuuki, the more explicit his rewards is, that's why Kyouka and Himari are the two girls doing the most extreme stuffs. That kind of bedroom progression really doesn't need to be explicitly stated, you can just observe the small changes with more time goes. Heck Kyouka feeling "being near his face is enough reason to kiss him" and Himari hearing his honest compliment and instead misunderstood it's about her body being "changed by him" is obvious enough show of progression already 😂
