I think it actually has to do with what is most read on Webnovel. Webnovel really seems to be focused on Light Novels, the Asian type. Now, do not get me wrong. There are a lot of kickass Japanese novels that describe the lives of heroines without any reference whatsoever to romantic relationships. However, when I think about Chinese YY novels, I really cannot think of one that was purely about the female character's life without any reference to romance. And Webnovel does have a very strong Chinese feel (I don't know where Webnovel's headquarters may be, but I would go with Indonesia, maybe).
All their premium novels marketed towards women follow the Chinese tropes of what makes a good girls' YY novel. What female readers of Webnovel want to read in great numbers seems to be romance. Often, with an easy plot (I am not looking down on anything; I love myself an easy plot more often than not). So of course, that is what Webnovel will try to market itself as: a source of heart-warming, fun, easy romance stories to read real quick without breaking your brain.
It all comes to choosing your platform. Each webnovel platform has its own specialty in a way. Asian-inspired novels are your cup of tea? You would come to Webnovel. You are looking for LGBTQ+/BL/GL (GL in a much smaller proportion)? You go to Tapas. And Wattpad β¦ I don't know what Wattpad's specialty is, but they must have one.