I'm on the fence. Since it's not restricted to fantasy and sci-fi, it's arguably off-topic anyhow, but is asking for a site that offers a particular sort of recommendation on topic?
I'd say these types of questions are off topic. It's a borderline recommendation question but it also falls somewhat into the following off topic categories:
every answer is equally valid: “What’s your favorite ______?”
Whilst it's not really asking for your favourite recommendation site, it is in a way, again borderline here though. But of course every answer here will be equally valid.
your answer is provided along with the question, and you expect more answers: “I use ______ for ______, what do you use?”
It is this type of question with the caveat of the ones the OP is using aren't quite fulfilling their needs.
The close reason itself is:
Requests for lists of works or recommendations are off-topic as they do not fit our questions and answers format. Feel free to ask about people's favorites in chat.
This is a recommendation question just not for lists of works but for a site that recommends books; still asking for recommendations though. The reason for why these questions are off topic is the same.
Note that for the reasons above even if we didn't have a specific close reason here I would say it is likely to be closed under "Opinion based" or "Needs more focus" anyway.