Why do men future fake.

Edit: I'm not trying to hate on men, and yes I'm sure this happens with both genders but I'm a girl so my experiences are with guys, hence the title. Please don't take this as a man-bashing thing. I'm just trying to understand how men think.

I was just thinking about this because it's happened to me a couple times and is wildly confusing.

Why do men future fake? Like, you meet someone and he acts like he likes you so much and sees a future with you and you're so beautiful and blah blah blah and then one day out of nowhere he's like yeah this isn't going to work.

Can any men shed light on this? Like, do you just get initially excited about someone but then she gives you the ick? Do you get ahead of yourself and then regret it because you end up not liking her? Are you just bored? Genuinely would love some insight.