Why do girls lose interest, when a guy is being nice to them?

This is not about the good guy vs bad guy feud. I mean when you're trying to help a her, listen to her, and basically be genuinely nice person. They eventually lose interest. Almost always.
Whereas, if you're treating her normally, you probably have a better chance. in the beginning of the relationship I mean. I think most of the time you'd get friendzone-ed for being nice.
Why do girls lose interest, when a guy is being nice to them?
Post Opinion