What kind of torch?
It doesn't take a lot of energy to make a 14 gauge piece of steel glow, but to make a 3/16, 1/4 or 3/8" sheet glow takes a bunch more (heat) energy, and more importantly, time, both to heat up and cool down. This is without considering how you're changing the internal structure of the metal by heating it up.
Finally, the torch costs $, as does the fuel to run the torch. I imagine it'd be easier to build a press that can form whatever thickness steel you want than it would to heat each sheet, otherwise we'd see larger machine shops / fab shops practice preheating before bending (we don't).