[Matt 'Maverick' Watts]

One of the main reasons paintball fields have limits is their insurance policies. Insurance companies dictate what the on-field velocity and bps paintball/airsoft guns can shoot at. If fields violate that, their insurance becomes null and void.
These insurance policies are also why you see a lot of 'paintball-approved goggles only' at fields. It's not the fields being idiots, it's the insurance companies.