can somebody explain to me why there are people queing for support and going mid lane builds

Some people decided that, since it's easier to get support and some mid laners can support, that they will just do that and get what they want every time. Some streamer probably mentioned it or something and a bunch of people jumped on the idea.

All I can say is now is a great time to play very safe marksmen down bot lane, because a lot of supports right now don't actually know how to support.

because they are probably using outdated build strategies from shit sites or trying to imitate pros without watching what they actually do.

For example if you see endgame stats where in bot there was

ok so something is unusual here but some noobs will just see this and copy it without ever investigating to find out that graves was constantly in enemy jungle helping kindred and blitz would leave graves solobot to gank mid whenever he got the chance. They don't see this but they see the pro build and just copy it without a thought

veigar support rules

I mean, there are a few that can do so. Zyra comes to mind (as long as she fucking gets a sightstone at some point of the game g'damnit). Otherwise yeah.

because they are assholes