Depends on who you ask, but I think the biggest reasons:

• they seem to have contributed to making people dumber indirectly. You see a lot of street videos of people asking questions like where is this state or that country and they can’t answer those questions but they can tell you almost anything about the Kardashians. Because of that, some people hate the Kardashians.
• they’re rich and have no worries. On one hand, you have some people who hate for jealousy and others who think it’s gross how rich these people are.
• the reason why they’re famous. On the one hand, the late father was one of the lawyers in the OJ Simpson case, but the real reason for their more recent fame comes from Kim doing a sex tape and getting famous off that. To some people, that’s gross and a stupid reason to be famous compared to someone else who finds a cure or does work in the community or just someone who actually worked for their fame like a movie star or famous writer.
• the Kardashians are kind of a nasty bunch of divas. I mean, if you have seen some of the clips, you can see that most of them are not really good people who care about other people but themselves and their fame. And the people they’re connected to aren’t the greatest people either which speaks more about who they are as a family.
• the fact that they are famous at all. To some people, it pisses them off that the Kardashians get a spotlight at all.
• scandals. Caitlyn Jenner is an extension of the family but the accident and death resulting from it and barely a slap on the wrist is worth hatred from some people. Scandals like those are among the family. You also have conspiracy theories like what happened to Lamar Odom’s death and some thinking they had something to do with it.

A whole lot of possible reasons depending on who you talk to.