I’m guessing the logic is to adhere to the game’s core principle: everything happens diegetically through a mail UI, which would make it weird for the two characters to engage in mailing while being in the act. This might be due to the library the game runs on, which seems to be designed primarily for narrative games. That said, if I remember correctly, there was a very similar game where you chatted with your coworkers and, in that game, they circumvented the principle by having the girl send the main character a video (or was it pictures?) of themselves having sex after the act. So, even here, there’s a possibility. But it could also be that the artist isn’t comfortable yet drawing actual sex scenes—who knows?
