Just saw that when I last commented about this topic, it wasn't actually in the Suggestions forum. [link to people commenting and generally agreeing here]

Basically there's no good reason to split them and it just gets confusing.

Same with shounen ai and yaoi

Are you aware that difference between shoujo/shounen-ai and Yuri/yaoi is almost the same as for shoujo/shounen and josei/seinen? -ai is mostly around pg15 while Yuri/yaoi is always 18/19+

Because if it will be merged shoujo+josei and shounen+swinen also should be merged

Quote from Nyxsha

Are you aware that difference between shoujo/shounen-ai and Yuri/yaoi is almost the same as for shoujo/shounen and josei/seinen? -ai is mostly around pg15 while Yuri/yaoi is always 18/19+

Because if it will be merged shoujo+josei and shounen+swinen also should be merged

This is completely wrong. Shoujo, shounen, josei and seinen are demographics and describe the target audience -- they're not an inherent indication of content (Banana Fish is a shoujo manga, Pandora Hearts is a shounen manga, etc). It's all to do with what magazine they ran in and what label they're released under. MU and most anime/manga sites use these as genre tags when really they're not.

The shounen ai/shoujo ai and yaoi/yuri distinction is something entirely made up by the English-speaking world. Japanese does not use the former at all, yaoi was used but isn't anymore, and yuri is still used sometimes. But both have been superseded by BL (Boys' Love) and GL (Girls' Love).

Surprise, this is an English-speaking site. Also, I've seen Yuri being used more than GL by the Japanese.

I don't see the use of it being merged when basically everyone in the English-speaking community knows what the distinctions are. Unless MU wants to add a proper age rating system rather than just "Hentai" or "Mature" (which are just wishy-washy tags) like how Mangadex did, merging them right now doesn't have any benefits.