Imagine: They're on a super low-end chip, feeding a bufferless DAC, and they're experiencing buffer under-runs, which cause really noticeable degradation ?
Imagine: They're using some API so wrong that it "works by accident" but only really when timings are "just so" ?
I've had thinkpads in the past that would output varying degrees of noise on the analog line+headphone outputs. It was highly dependent on what the CPU was doing, how much data it was moving around. It was kind of fun as a sort of audible system instrumentation while developing/testing software. The more optimal I'd get things, the higher pitched the noise became.
But no "audiophile" should be using such cheesy analog output from a computer... At least get some S/PDIF off to the fancy preamp.
Go back 10 years and many laptops had issues with cpu frequency scaling and sound quality. (Cheap components that would either start producing audible or em noise that would impact sound)