When it comes to whoever becomes a sex symbol, especially among geeky cishet women, there are the more obvious choices then comes the more unexpected ones. There are some women who’re (sexually) attracted to the actor Christian Bale, but it’s Adam Driver who’s become an unexpected geek sex symbol mostly because he’s so unlike most actors we’ve come and known. I could say many of the same things about Benedict Cumberbatch and Tom Hiddleston, two men whose roles have made them into Tumblr sex symbols.
When it comes to fictional characters, there are also unexpected cases where in the case with the video game Undertale while many of the characters also got sexualised by fans it’s Sans who’s become a major male fandom sex symbol in a way that Mettaton hasn’t. When it comes to what some women are into, they’re not always beholden to what’s expected of them to be into. Some women aren’t into muscular or fat men, some women aren’t into tall men either.
Then there are men het women aren’t supposed to be attracted to in any way, which probably accounts for why Tumblr sexymen become the way they do. Some of these characters aren’t buff, some of them tend to be thirsted after whenever they tend to be skinny and appear in a suit. Dick Grayson is sexy, but he’s not a sexyman the same way Riddler and Venom have become. That doesn’t stop Grayson and his ilk from being the subject of many slash fanfics, but when it comes to sexymen they’re a class of their own.
They’re pretty much major geek sex symbols in a way the more conventionally attractive men aren’t, not that they aren’t unattractive but they don’t garner a big, defensive fanbase the way these characters do.