Righto, I haven’t used a desktop in 15 years, and I can’t imagine why anyone would.
I usually run it hooked up to two large monitors, plus the notebook screen, and a keyboard and mouse. But why wouldn’t I want to be able to take it with me if I want to?
Sure, let's run the FR server on a tablet, no problem.
And try to cram a specialized scientific data acquisition card (or numerous others) into a laptop.
Not everyone has your modest consumer-level requirements.