Why Are Only Marksman/Support Combos Played Botlane?

The thought of it is that the support feeds the marksman kills and farm while protecting and babysitting the marksman into mid and late game because all marksmen are late game DPS carries while being weak early on.

But there are so many other different champions who could make use of the same kind of protection that a support grants you. Cassio and Azir come to mind, both Champions who need to farm up first and who become super strong in the late game.

Also, when you expect the enemy to always pick a marksman and a support, you could theoretically use a combination of a burst mage and a cc champion to counter them. Let's say something like LeBlanc and Leona, it would be a total nightmare for an enemy marksman, especially for the immobile kind we often see right now.

I'm just wondering because from my experience, the solo lanes make much more use of weaknesses and counter matchups. In top lane you can see everything from marksmen to mages to bruisers to full tanks and counter matchups are super important. I think in the midlane there is a similar variety though I don't really know much about it.

Yeah, there was Mordekaiser but that only happened because he was grossly overpowered and just has been forced down there in a very experimental way. But considering that Marksmen and Supports both have obvious weaknesses and strengths, I'm just confused as to why no one has ever tried to exploit them.

I might try one of these combs myself if some of my friends are actually willing to do that. I'm going to write about it here after I've done that.