I can understand your point, to an extent, but do try to see it from the other side as well.
Have you ever attempted to Solo Queue as ADC or Support by your lonesome?
Being chained to a random stranger who may or may not be a mildly sentient brick with thumbs is a joy that only solo bot players have to face.
Even if the support/ADC is competent, if you have divergent play-styles (aggression/passivity/target selection/dives) even an individually competent duo might function about as well as a quadriplegic tap dancer.
Should an already irritating/stressful role, in which every champ on the map is designed to make you cease to exist, also mandate that you MUST queue with a random stranger? Better sacrifice a few virgins to the deity of your choice whenever you queue up, you're going to need some luck.