Thanks for the TL.
Why does a kiss feel more lewd than upskirts and cleavage shots?
I think is because you could find those things easily in any sort of random ecchi manga or on Pixiv/Deviantart, but here you actually care and got to know the characters. The great perks of having a post-confession story, which also feels more intimate than all those harem with accidental nudity.
What does it mean for the heart to peer at a naked girl bathing? We are an intruder, there is no connection between characters happening, no development, no progress, we are simply intruding in a moment of vulnerability where she chooses to be alone, so there is a mental barrier.
Here we have the meeting of two forces that want to join together, is the soil reaching for the seed.
Also, it could be like
Junomano said too, perhaps we implicitly recognize it as the preliminary action that precedes coitus.