They never set out to build the ultimate power user machine, their target was still general consumers. They just happened to have the right product at the right time when everything else just failed to compete.
Had desktop linux been in a better state, or had MS built WSL earlier, things might look a lot different today.
Here's a Titanium PowerBook G4 ad that says "Sends other Unix boxes to /dev/null": https://www.reddit.com/r/vintageunix/comments/b4kojo/sends_o...
Here's a snapshot of the software solutions page for the aluminum PowerBook G4 from November 2004, proudly touting Unix and even X11:
https://web.archive.org/web/20041126011836/http://www.apple....
Some quotes from the Power Mac G5 page (https://web.archive.org/web/20041126015955/http://www.apple....) from the same era:
"With the Power Mac G5, a researcher can now run both productivity applications and high-performance UNIX applications on a single system. Mac OS X Panther includes 64-bit optimized system math, vector and image libraries that take maximum advantage of the 64-bit G5 processor."
There was also a cluster in Virginia made of Power Mac G5s, which Apple also touted.
Microsoft had "WSL" earlier, only badly.
The only reason I started with Linux at home back in 1995, was the half hearted UNIX subsystem on Windows NT.
Had they been serious about it I am sure GNU/Linux would never taken off.
As shown by Apple sales of folks buying POSIX instead.