I think ROT's are used much more often than actual loads. So called "older guys" will say they've been doing it this way for years and why should I tie up my time with a load just to lose the job to another contractor.
I think younger contractors are much more likely to do a load because they are more familiar with computers and more comfortable with the results. Computers seem like a natural place to get information for them.
I often see posts here looking for load software when it's just as ez with a simple paper form but they've learned to trust computers. I'm sure it's easier to get an older contractor to use the paper form than a computer. Different generations.
I wouldn't expect many older contractors to change any time soon. Their system will probably work ok and no one's going to yank it out to show how a different system will be better as long as the house is fundamentally similar to those where ROT worked before.
Here in California, plan checkers are becoming strict and asking for Manual D & J. For energy purposes, the state won't let you install a new HVAC without load calcs and making sure the unit is not oversized.