Energy. Lasers are hooked to the power grid. My guess is that battery lasers would not cut thru steel. Or it could cut thru steel for about 2 seconds then need a recharge.
So as we come across Higher output, quicker charge batteries such as the one being developed by Musk, or the Graphene Battery, we might see an answer to the energy issue.
Would the “steel cutting” Laser maintain its lethality at 50-60 yards, or 100 yards?