I don't know if V Twins are the current default engine configuration for most street bikes, inline 4's are still the big sellers from most manufacturers, but V twins became popular in early superbike racing, because Ducati dominated for two reasons; they were much narrower than their inline four cylinder opponents which gave them increased lean angles and faster cornering, and were allowed extra capacity to compete with inline fours BHP, so could run up to 1000cc bikes against 750's, which gave them a torque advantage that won races on tight circuits.
Suzuki and Honda quickly built V twins to compete with Ducati, and after some initial teething issues, Suzuki turned their V twins into a successful franchise, with both road and "dual purpose" 1000cc and 650cc twins, which are very popular today. A friend of mine has a Honda VTR1000 and I rode it for the first time last weekend, and loved it. Apart from the riding position which I find a little cramped, it's a great bike, and now on my bucket list. Cheers, Terry.