Because I like the hardware but despise the software. I haven't found another laptop that comes close, although I don't have the money to try many.

Not only that, but in the F500 companies I've worked for it's not uncommon for employees to get the latest shiny new thing when their existing machine still has lots of life left. Repurposing it with Linux means I can use it.

Because the hardware is actually good?

Because there is no comparable hardware to be had for any amount of money anywhere.