Because in stead of spawning in as a selected class like you would in a normal game, you can in stead change weapons on the fly; convenient right?
Except that all the weapons are without any specializations. There is literally zero point to accurately learning recoil patterns if you can't include the effect of reduced horizontal recoil (which is something you're going to pick 99% of the time when it's available), and to a lesser extent vertical recoil. The whole point of practicing something like this is consistency, and if the recoil parameters are vastly different on the range then it's actually detrimental to your performance because you're simply learning yourself bad muscle memory. Funnily enough, the vehicles you spawn seem to have specializations.