The majority of men do expect and prefer that women are shaved, thus the assumption.
You know, I wasn't going to call it out in my original comment because it was beside the overall point, but "geeksandmisandry" and now you are interestingly assuming the gender of an anonymous user with a default pfp and the gender-neutral username "dinogatrr".
I don't think even if they were a man that this would be a good reason to assume they're a shitty person (especially because the sample of "men on Tumblr" is going to be vastly different than "men overall" or even "men on social media overall"). But it is an interesting assumption on top of an assumption: they're a man, and they're a shitty person who thinks women's legs are naturally icky.