So I looked up the Raptor Talos II. It's a $7k (starting price) workstation running IBM Power9 RISC based CPUs which are typically used in super computers.
OOC why would someone want to use such a niche architecture for their primary workstation vs say an AMD Epyc or Intel equivalent?
POWER9 has some deployment in supercomputer clusters but its primary use is in IBM servers, basically the modern descendant of IBM minicomputers. These are purchased by businesses that want to run IBM i or AIX (or Linux).
https://libreboot.org/ https://coreboot.org/ https://boingboing.net/2012/01/10/lockdown.html
Financially supporting a nascent open source hardware movement seems like a good thing.
The asker has already decided what matters, what doesn't matter, and why.
The answer "Because X matters." is as meaningless as the question "Why does X matter when X doesn't matter?".
It's a thoughtless and effortless question that expects a thoughtful answer which is not effortless.
The answer is these three assertions which you will have to just accept as given. Your question exposes that you have either never taken 5 minutes to think about things like this, or have, and arrived at some other conclusion, and so would not make these assertions yourself. That explains why open source doesn't impact your product decisions. You asked why it impacts anyone's.:
1 - One doesn't need to do a thing personally to benefit from, or value the fact that a thing is possible, nor to appreciate the difference between possible (however difficult) and not-possible, nor the difference between natural and artificial difficulty or impossibility.
2 - It matters who ultimately controls ones possessions, and through them ones life.
3 - Ideals matter.
Supporting owner-controlled computing was one point, but I also really like toying around with exotic systems, especially if they've got UNIX heritage :)
Clearly this is hobbiest for him in at lease some ways.
There are cheaper models, "down" to $4k, probably around $3k if you build it yourself; that's still expensive of course, but less :-)
(I wasn't able to read the linked article, so perhaps he indeed describes the version matching the price you quote, I don't know.)