Tube Cutting
Voortman is able to import DXF files. They can be used to create 3-D shapes as long the steel has been detailed according to certain rules. You might need to adjust some of these rules to match the details you are currently using. This process may not be as seamless as 3-D modeling software.
Of course, the most important reason is price. High-carcinogenic dust from plasma cutting must be collected in a dust extraction filtering unit. The price of fully enclosing the machine to evacuate dust is much higher than what a typical fabricator can afford for a beam handling solution.