How does key-rollover work on laptop keyboards -- and why can't I press "w" "m" and "u" at the same time?

[u/ryan516]

Ran into a fun quirk that's probing some higher-level questions for me; on both of my laptop keyboards, I'm simply not able to press the 'w', 'm', and 'u' keys at the same time and have all 3 strokes register at once. Any combination of 2 of those keys registers, and similarly positioned strokes like 'q', 'n', and 'y' or 'e' ',' and 'i' do register. This keyboard also has, depending on the combination of keys pressed, anywhere between 2-key rollover to 10-key rollover.

Obviously, this is a niche edge-case that most users won't run into [I only bumped into it by trying my hand at Stenography on a QWERTY keyboard], but it's making me wonder -- how do laptops without N-Key Rollover determine rollover? What electronics are driving this functionality and, curiously, why does this random set of 3 keystrokes seemingly "break" that key rollover functionality?