AD carry + support lanes started off because AD carries were weak early game
Back when this meta started the standard ADC was like Ashe.
Now, AD + support lanes are the best 2v2 lanes in the game and no other 2v2 lane can counter ADC support lanes. You can come up with any combination of bruiser/support/mage/assassin and they won't beat the best ADC + support lanes.
Not to mention ADC support lanes outscale everything else. Riot has been powercreeping the early games of AD carries ever since Season 2. Graves, Draven, and now Lucian, etc
This is a fundamental problem that needs to be addressed. This is the main reason AD + support lanes are so standard, because nothing beats them