I think there are a few different reasons;
- A small very vocal minority of "feminists" have taken the cause too far and are finding sexism where it really doesn't exist. As someone else said, whoever shouts the loudest will be heard. I think there's also women who use feminism to garner attention and justify behaviour which is clearly just to seek attention e.g. Kim Kardashian and Emily Ratajkowski posting naked selfies and pretending it's part of some crusade for women's rights, when in reality it's to further their own careers and attract more attention.
-Many men simply feel there is no need for feminism anymore (in this country at least). I think male privilege does come into play here as many things which are sexist simply do not affect men or men do not consider them to be sexist, therefore they don't see them and downplay or dismiss sexism. The same way a white person will be blind to a lot of racism because it's something they have never or rarely experience and may downplay or dismiss acts of racism or believe they are rare isolated incidents.
-There is an attitude of "well there are things which are sexist against men so you have no cause for complaint". I agree that there are laws and attitudes which are sexist against men, particularly when it comes to fathers rights. However, if you look more in depth at this, you will realise that these laws were created almost exclusively by men and are due to child rearing being seen as "women's work" and something women are naturally better at. Society still at large believes that women should have the responsibility of raising children while men should go out and work. Women are being blamed for "unfair" laws against men when most if not all the laws in this country were created and decided upon by men. Also, remember that most judges are men. If men are getting unfair treatment in the courts it's usually due to other men not women.
-A small amount of men are angry that women are trying to or have "stopped" them from doing things they believe they should be entitled to do. They may believe they are entitled to be sexist under the banner of "freedom of speech" and "having their own opinions" and women who object are being too sensitive or are "feminazis" and "man haters". Some don't even realise they are being sexist. It doesn't help when there are a lot of women also making sexist comments and using derogatory language against other women, as it reinforces the opinion that it is acceptable and correct in our society e.g the different attitudes towards promiscuity between men and women, I think women get judged just as harshly by other women as they do men in regards to this. Women should stand together instead of dragging each other down.
I think there are wrongs on both sides of the debate, but by in large, most people, men and women are for equal rights. It's a shame that feminisim is misunderstood and has become a dirty word, many people now refute being called a feminist despite actually agreeing with what feminism ultimately stands for, which is equal rights for men and women.