They don't - the downvotes (none of them mine) are because this is a somewhat dismissive mischaracterisation of the issue.
No reasonable person or group objects to discussion about issues that affect men. What they do object to—quite reasonably—is the often-associated attitude which runs along the lines of "Men suffer from <any problem> too, it's not a feminist thing!", which isn't really helpful.
The idea suggested by this article is that men are actually approximately as likely to suffer from sexual assault as women are. That's a perfectly valid possibility, and it's likely true.
But what's the general goal of a "feminist," if you can use such a broad term? Let's keep it simple, and say that "a feminist's goal is to further the cause of equal rights for women." Given that, why would we expect feminists to be talking about the effect of sexual assault on males? It's not their responsibility to do so, and I'm absolutely certain that most feminists would not object to male campaign groups which highlight the problem of male sexual assault. The problems which affect both genders, even in this area, are actually quite different!
The problem with these discussions is the ease with which one can focus on outspoken minority groups. The vast, VAST majority of feminists are not "anti-male"; that vast majority of men are not anti-feminism. It's easy to get carried away by overemphasising the views of minority groups.
Your comment is ultimately a meta version of that - in truth, there's very little opposition to discussing men's issues, but instead a fair bit of opposition to discarding womens' issues because "men have it bad too."