"Manga where MC and FMC already a couple is not interesting"
How so wrong for those who say that. If the relationship is wholesome, people will love it (Insulin shoots required in most case)
There are some reasons for it:
1. It’s harder to write
2. Just-sugar is nice, but just-Drama sells better, (if the writing is equally simplistic)
3. Some celibate people can be veeeerrryyyy petty and nasty
The Manga market tries its best to not combine the demographic of hinting at (wholesome) relationships with demographic actually interested in (wholesome) relationships.