Why is it that guys always come back after they decide they're not ready for you

I met three guys last year who I had great connections with. The first (A), I dated for three months, though I knew he had stopped seeing anyone else while with me. There had been stresses or whatnot in his life at the time, and oneday, he decided he wasn’t ready. I adored him heaps and struggled a lot, but accepted it and let it go. Four months down the line, he returns from his out of town job and wants to apologise in person. I accept. We have open conversations. He has since stepped up and shown me he can make the effort. I let him back in and we have been going really well since.

While A was gone, I dated other guys. One of them was B. He was travelling and I knew meeting up with him would be a no strings attached affair. We ended up getting on very well on the first date, and as much as we tried to not get attached, we did. We ended up staying with eachother for the night. We exchanged many emails and texts after he went back home. We knew we had something going but it was silly to make it possible. After a month or so, we ceased contact. Six months later, he contacts me out of the blue to ask how I am. I let him know that I am now seeing someone, A.

I had also met C, while A was gone. With C it was a perfect date. We saw eachother for a couple more dates after the first. Sexual chemistry was high so I couldn’t hold back. We exchanged a few texts after the last date, then it fizzled out. I let it be. I didn’t initiate further texts. Neither did he. I figured he was more interested in sex. Again I moved on. Six months later, he friends me on fb.

I had left things on good terms with all these guys and genuinely really liked all of them. But when they decided they hadn’t wanted me in their lives, I didn’t rebel, wasn’t angry about it. If they can’t show that they want to have me around, there is no point in me persisting.

But why had it taken each one of them a timeframe of around six months to decide they want to get in touch again? What is their reason for getting in touch? I’m not interested in pursuing anything with B or C, but I’d like to understand what goes on in their minds the point at which they suddenly decide to want to know you again?