here's how fill works

supply/demand. if you need me to explain that to you, you're hopeless.

i'll explain it anyway.

you see, there's a very low influx of support players deliberately queueing as support.

in comparison, there is a large influx of players queueing for ADC, Top, Mid, and JG.

so you see, when you select fill, it's going to get you a group as fast as possible based on what the team comp needs/ is short of.

HENCE WHY FILLING GETS YOU SUPP MOST OF THE TIME.

don't wanna play the role very few other players pick? DON'T FUCKING PICK FILL. simple. the system is fine, just the people crying about it are RETARDED