Long time geek, fangirl, mother, and reader. I've got a lot to say, you might not like it all, but it will be honest and hopefully helpful.
Trigger/Content Warnings are meant to announce the presence of content that might illicit a strong or potentially harmful emotional response. They are used for things like rape, incest, blood, and animal death. Demanding that authors warn readers about characters' sexual orientations, certain kinds of sexuality, or non-binary genders, etc in the same way we treat traumatizing things like rape implies they are equally damaging, when they are ABSOLUTELY NOT!
Trigger/Content Warnings were not meant to be used as a laundry list of content that readers' dislikes and demand authors warn them away from. Not liking to read about oral sex, or not being interested in reading about lesbians is not remotely the same as wanting to avoid being trigger by graphic violence or pedophilia. It's insulting to ever put these things on the same level.
An author writing in a genre you don't like has no obligation to inform you away from their work if it doesn't contain anything harmful.
If you suffer from the misconception that everyone is cis, heterosexual and monogamous unless they explicitly state otherwise that's YOUR problem. You have no right to demand other people accommodate your ignorance.