Because CRTs (and maybe other displays) are slaved to the input and insensitive to exact timing, and console chipset designers used convenient line counts/clock frequencies, consoles often have frame rates slightly different from standard NTSC (which is 60000/1001 or ~59.94 fields per second).

The 262 AND A HALF lines per field NTSC uses to get the dumb oscillator in a CRT to produce interlacing, is not convenient. “240p” moves the VSYNC pulse, shortening the frame duration.

So NES’s run at -60.1 FPS.