People Always SoloDiving in ARAM?

I don't really understand it, a majority of the games I lost /or had a bad game in ARAM were because 1-2 people constantly diving alone, and I'm not just talking about bots, but those are a huge problem as well. Some of these are just as bad as bots when they refuse to work with the team at all and prefer to 1v5.

They either dive 1v5 and wait for no one on our team, or they wait until our entire team is dead and then they try to 1v5. I had a Lee Sin that would Q into them every time he respawned, and not once try to get away with his W or Flash. I just had a game with Lee and Xin diving constantly without the team anywhere near them. It's not always my team, but these players in general kind of ruin the match because if the team is smart they just take advantage of the free kills.

It's more than just getting 'caught out' and permastunned, they go full all in 1v5 an entire screen's distance away from the rest of our team. I even politely ask 'Stay with the team plz we got this' and all this seems to do is encourage them to flame and blame our loss/them doing badly on me. I never actually get angry at them, except for a few rare occasions where that's literally all they did the entire game was just dive over and over at every time they respawn, and even then I am relatively polite. The worst I ever said was telling them 'you're making this a 3v5 by not staying with the team at all, please stay with us' of course I know this pretty much will never work even if I'm polite, but at least I have evidence if they're doing it to the extent that I consider reporting them.

Can you think of a better reason other than "It's just ARAM, people can feed if they want to"? I know it's not taken as seriously as SR, but the objective is still to win. I don't see what's fun about ignoring your team and trying to 1v5 when you're not even fed at all.