I think it's cause all the sex scenes before did something for the plot. Like they changed the dynamic between the main characters, or confronted how they felt/acted during heat/rut, every sex scene was a step closer for them in a sense. We already had the sex scene that 'establishes' them as a newly lovey couple, so now it seems like Ok this is more of that then, and it kinda stalls. Especially since nothing else is really happening like emotionally for them, they've been on this date for years it feels like lol. Before there was a lot of emotional questioning between the sex scenes, now not so much.
yeah the sex scenes furthered the plot before because they didn't like each other in the beginning but now were getting more and more of them and it sort of feels like fanservice? I ain't mad at it tho i'm an equal opportunity pervert, but usually i like my yaoi to have a good story or else it just feels like i'm reading smut or a doujinshi.
don't get me wrong i like the fact that there are sex scenes but i miss when this webtoon had a story ┗( T﹏T )┛ its like we get 1 chap of story for every 3 chaps of sex scenes.