If you want to fight for euqality it makes sense to fight for the rights of those who are currently discriminated against. Women, even in developed countries still are such a group in key social and economic issues.
I do not deny that there are perhaps some areas where men face discrimination as well of course and that they need to be addressed as well, but on the whole it's pretty much undebatable that women are worse off. Not to speak of the situation in some developing countries, where women still are often regarded as not much more than objects.
Fighting for women's rights is fighting for human rights.