Why is yumeshipping so disliked?

I fouund out what being a yumeshipper is not so long ago and I noticed that a lot people that said they are yumeshippers get a lot of hate, and I really don't understand why? I don't know if it's because they can be considered problematic or anything like that but shipping yourself with fictional characters or shipping your oc's with them has existed for so long just without an actual name to it. Maybe it's not as hated as I think but so far every time i've seen someone say that they are yumeshippers with x character they inmediatly start defending themselves or saying how they don't care about the hate. So i'm a little confused, why is it so hated??