People, for some kind of reason, really like their laptops. They also have more brand recognition, thus the "bragging right" part, when you get your new X1/Macbook every 2 years.

And if you still work on your laptop but have your personal server box as a CPU slave, that still leaves some issues. You might be able to do your build steps on the machine, but your IDE still runs on your laptop, so that needs to be beefy enough -- never mind auxiliary applications like browsers, Photoshop, CAD etc. Also, it's quite hard to get a slow laptop with decent ergonomics, unless you buy used (not that much an option for companies).

Also, once you go headless server, it's better to just put it online anyway, as you don't need 24/7 access