Welding with current typically requires electrric arc. That typically requires some gas at high enough pressure. Welding in space would mean you need a lot of g

Welding with current typically requires electrric arc. That typically requires some gas at high enough pressure. Welding in space would mean you need a lot of gas, which has to be shipped from earth and it's pretty hard to keep enough pressure near weld when you're in vacuum. Lasers have the smallest heat affected zone of all welding, so you need to get rid of smaller amount of heat after welding, pretty usable when you don't have atmosphere around you to cool your welds.