I haven't read a ton of fics with ace characters, but I've found a few of the ones I have read boring because it was more about the fic being a soapbox for How Asexuality Works For Everyone. Which is obviously untrue, as it doesn't work the same way for all ace people (or characters).
I find fics that do the same thing for queerness or transness similarly boring. I think sometimes it's people who hold those identities themselves and are really invested in their own narrative to the point where in order to have their narrative accepted they thing the way to do it is to press it on others as the only acceptable narrative. Although also I think it's often people who don't hold those identities, but have read whatever dominant mainstream discourse on that identity and therefore decide, "Aha, this is how this thing works for everyone! I will write a fic to Teach Others about this and lecture them about how deviating from this norm is Very Wrong."
no subject
I find fics that do the same thing for queerness or transness similarly boring. I think sometimes it's people who hold those identities themselves and are really invested in their own narrative to the point where in order to have their narrative accepted they thing the way to do it is to press it on others as the only acceptable narrative. Although also I think it's often people who don't hold those identities, but have read whatever dominant mainstream discourse on that identity and therefore decide, "Aha, this is how this thing works for everyone! I will write a fic to Teach Others about this and lecture them about how deviating from this norm is Very Wrong."