I have had this happen to me on several occasions please allow me to get a few off my chest!
My first serious boyfriend who I dated from 15 to 17 dumped me because he had met a "better prospect" at uni and wanted to be free to persue her. I was hurt of course but fair enough. When his better prospect failed to pan out he thought he'd just go back to me but luckily I'd moved quickly as you do at that age. In the next few years anytime I met him or he sought me out he'd want to get together and catch up, when I refused he'd resort to telling me that I used to be nice but had turned into a real bitch ... nice! Luckily I haven't seen him for a decade now.
Boy I was friends with at uni and liked was never interested in me because I wasn't hot enough fair enough, a few years after uni he writes to me out of the blue announcing that he is in love with me, always has been 
. When I write back to tell him thanks but no thanks as I'm already taken I get hit with a barrage of insults (in my experiance insults are par for the course when you reject a man for what ever reason).
Another guy I went out with at uni and who I'll admit I was crazy about wouldn't commit to me in anyway because quite frankly I wasn't Bjork and he felt he was destined to be with her. He still sniffs around every once in a while boohooing about his "mistake" totally disregarding the fact that I am married and have been for well over 10 years.
Ditto for another toxic boyfriend I had before I met my husband, he was your typical sexy bad boy back in the day but is a totaly gross middle aged pothead now and yet still thinks I secretly long for him, deluded.
With some exceptions, I agree that it is all about ego for these men and nothing to do with us at all. In most cases they are looking for an ego boost, sex or a fallback position and some of us might even have given into them in the past because we loved them but I don't think thats a healthy position to be in.
After all my dealing with arseholes it was such a revelation to me to be with a man (my now husband) who wasn't looking over my shoulder for the next best thing for whom I was the prize and thats the way it be.
Interestingly every single man I've listed here is still single and they will all be between 40 and 43, I must have had duff taste back then!
I would say that yes in the past at low ebbs or when single I have thought about past boyfriends and crushes and wondered where and how they are. The difference is that I never went as far as contacting any of them because while felt tempted to see them I realised that they had moved on and most likely had zero interest in seeing me again.
For these men who do think getting back in touch is a good idea must have very poor emotional intelligence. It is like they think that because they are thinking about you, you must be thinking of or hankering after them, or that they are so amazing you would happily drop your husband / family to be with them. Its just so infantile and creepy and if they ever did get you back don't expect them to trreat you with any respect you'd just be another one on the line.
With that said I am sure there are notable exceptions to these men but I'd think they are quite rare.