Whilst watching yesterday's Starliner launch I've noticed how skinny that Centaur (3.1m) looks compared to the CST-100 (4.5m).
Looking up the Atlas V I was amazed to find out that it has even larger (5m) fairing as part of its design (although protruding all the way down to the thicker first stage).
Apparently, apart from Atlas V and Falcon 9/heavy, there are quite a few of launcher designs utilizing this feature (fairing larger in diameter than the booster it is attached to), whilst others (like Delta IV, Proton-M, etc.) are designed with booster and fairing diameters matching.
There must be reasons as to why they don't design those launchers with booster diameter to match the fairing.
What would those reasons be?
Update: found this tightly related question about Falcon 9 specifically. The answer mentions that the booster diameter was limited in order to conveniently (and less expensively) move the hardware by road.
But there are many more examples of launch vehicles with boosters smaller than fairing. I am wondering are there any more reasons (structural, choice of propellant-wise, lifting capacity to LEO etc.) other than those related to transportation to launch pad.