There's a difference between attention and popularity. Drake, Kendrick, Cole, Future, Travis, Gunna, Carti, Baby, and Durk are more popular than nearly all women rappers. For every SexyRed, who is very popular, there are multiple Lattos and Coi Lerays who will always get more attention at an awards show shaking their ass than most dude rappers can muster. You could have J Cole performing at the BET Awards and it might not garner the response an Ice Spice performance garners, despite her not being particularly popular/successful.
In terms of male r&b...sure that shyt is largely dead on a mainstream level. I don't think it's a conspiracy, it seems pretty simple. I honestly think it's similar to why we don't see many elite black boxers or baseball players: kids who might have played those sports 30 years ago are exclusively playing football and basketball instead. Likewise I think a lot of artists who may have developed into true r&b singers find it more appealing to delve into rap or whatever you want to call the melody stuff (Gunna, Roddy Ricch, etc). These dudes aren't growing up listening to Usher, the way girls grow up listening to Beyonce/Rihanna/etc. They grow up listening to Drake and Future.