You can buy welding inverter device at every corner, just as SMPS PSU, look PC power supply 1-2KW.
Switchers are expensive devices on higher currents, can be really Bhut Jollokia in pockets.
Transformer based psu are almost undestructable devices and life time of this kind of power supply cannot be compared with SMPS. Also transformer based gives fine voltage output, compared with SMPS which have lots of ripples and spikes, which request additional filtering.
Welding device transformer AC/DC 180A can be around 55kg (good intermitenca-copper wires-high quality) and Inverter welding device of 180A can be 10kg. For portable variant what will you choose?
Also price of product will be higher if you use switching technology for power supply/welding device, cost of production, also needs better technical support-service. Iron transformer is simple to build and use, its reliable.