NTSC type CRTs has 525 scanned lines in interlaced mode, but not all are utilized for video info that we see. It has 480 lines, hence the 480i, 240 every 1/60 of sec. If that is in progressive mode you still have only 480p. Not sure where the link gets 540 lines. CRTs also have rasters and color phosphor that the beam excites. These are also of fixed size and number.
A CRT that displays more must have smaller holed in the rasters and more colored phosphors to excite to display. Some could accept other video signals and internally scale it to the TVs display capability. So, in essence, a CRT also has a designed in limits of resolution.
But, I could be way off