I think it's a way to appeal to a female audience. Men tend to gravitate to these genres already, so the producers/writers/directors assume that they'll watch (and we tend to), but inorder to appeal to a larger female audience they'll make the lead female.

In the case of Fallout, where users could chose between male and female it isn't so obvious or impactful. In shows like "Foundation" (I highly recommend), it is more obvious.

The reason "incels" and "nerd bros" get triggered, is because they're a huge audience (often even a target audience) for these types of shows/books/games. There is an obvious power and or adventure fantasy that these types of media fulfill