Maybe things have changed, but for many years one of the goals of cylinder head design was to have turbulent, swirling, air/fuel mixture in the chamber. Why do you suppose that is not the case anymore?
the goal is to have small tight swirls inside the combustion chamber. you can achieve this with proper head design but only if you can create a predictable environment on the carb intake.
"directed" air (like the air that comes through a forward facing snorkel then dumped into an airbox) and "quiet" air (like in a monster airbox with little to no lid) is very predictable. although you would fuel each one differently, the air is going to be predictable enough that head work and porting can optimize the bike at all speeds and situations.
by mounting the carbs dorsally, the air now comes in for each head differently at say, under 30mph than it will at 80mph, and differently again when you take a sweeping corner at 70+.
cornering is one of the trickier things as now you have one carb exposed to the rushing air coming straight at it, and one carb eclipsed by the bike getting a different velocity of air at a different angle.
