Remember.. In the old days, monitors didn't have all the esoteric geometric controls (pincussion, trapezoid, rotation, linearity), let allow full width and height horizontal/vertical sizing!
I remember many a game (and have picked up a few with burn-in patterns to match) that left a good 1/2" gap around all sides of the tube untouched, or crunched to one corner of the screen.
You'd be hard pressed to find a game scaled to match the exact pixel ratio. Differences in magnetic location with respect to the earth, fluctations in power line frequency and of course, drift due to heat/use of the tube overtime, it would have been dumb for mfg's, let alone arcade owners adjust a tube so the pattern filled the screen 100% edge to edge, even if the hardware had allowed them to do it. Because they'd be spending time every few weeks adjusting them back onto the screen, because if the playfield was clipped, you're not going to get someone dropping quarters in!
I frequently remember seeing MoonPatrol appear in a SQUARE screen (almost like a vertical game drawn in the middle of a horizontal monitor!) rather than a wide horizontal one.
Looking at the awesome controls of the Electrohome G07 monitor that has all of 3 jumpers to set vertial and horizontal size, no wonder there were strange aspect ratios to the games we all remember playing!