Why do girls think they can get with the guys they previously rejected after we've improved ourselves?

Anonymous
I was fat when I started college and lacked the confidence to be successful with girls. I didn't have much success, and I got rejected by a female friend I asked out my freshman year. She was the only girl I asked out that entire academic year.

I realized that I was never going to be socially successful if I remained fat, so I joined a training studio and paid a ton of money to a trainer to help get me in shape. I've lost a ton of weight, and more importantly, I've totally changed my body composition so I'm lean and muscular, though not huge. My confidence is up as well, and I've started flirting and dating more girls as a result.

The thing is, the female friend who rejected me my freshman year and another girl who blew me off have started paying attention to me now and are trying to flirt. It's not flattering at all, it's just very off-putting and annoying. They both rejected me in one way or another, so why do they now believe that I want to be with them? Do they think I'll just be grateful to have some female attention, even though I'm no longer out of shape?
Why do girls think they can get with the guys they previously rejected after we've improved ourselves?
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