On a bigger (& or wider) boat, it allows the helmsman to sit well outboard
, in order to get a good view of what's up ahead, as well as viewing the sail trim at the same time. Especially with low cut/deck sweeper jibs.
Plus, to get that kind of ability with a single wheel
, it would have to be rather big. 5'-6' diameter minimum.
Which means that it would need a slot inletted into the cockpit
floor, so that the wheel is at the proper height for steering whe standing. And said recesses MUST be kept clear of lines & everything else, lest you jam the wheel.
So in addition to eating up cockpit
space, big wheels also reduce available headroom
in bunks which run underneath of the cockpit. Just the opposite of twin wheels.
Then, there's the aspect of a large wheel, essentially trapping the helmsman back aft. So that he's not really as much a party to what's going on in the cockpit, socially, & racing
Which, for entertaining, is huge. And also, it makes it tougher for someone to go back & relieve him, & or go back there to be coached on helming.
And if you have an open transom, then twin wheels really open up the traffic pattern from the stern, to everything else. Instead of having to clamber around the wheels.
Just have a look at some of the modern charter
fleet, & or any of the boats made in the last decade or so.
Transoms have gotten a Lot wider of late, & cockpits are designed much more with entertaining in mind, as opposed to purely for sailing.
Then, of course, it's a marketing/styling thing (read $ generation). Along with everyone "keeping up with the Jones's". Plus, all of the cool kids
(racers) are doing it (have been for decades). And most sailors harbor inner desires to dream of playing like the pro's do.