Being "in love" means I want to spend the rest of my life with you!
I have "feelings" for you means: You are not (the one)!
It's the same thing as saying, "I love you but I'm not in love with you." (You are not "the one"!)
Statements like those are designed to freeze a relationship or keep the status quo. It's tossing a crumb of hope to somone that desires the whole cake. If the relationship goes south the person can always remind their mate that they (told them) they were (not) "in love". Until that day arrives you get to keep having sex with them, enjoy their company, and hold onto their friendship. Essentially it's wasting their time. If you know you can't give a person the love and emotional investment they want you may as well set them free. Time is something we can't get back.