problem is..IBM and all other machines were already conforming to COmputer screens and saw the Amiga as a Toy! Big mistake........
VGA said goodbye to low resolution displays. Sure, you need additional hardware if you want genlock, composite video, etc. But many Amiga users have additional hardware just for the sake of having a readable workbench (scandoubler/deinterlacer, graphics card)
Also note that 640x480, 800x600, etc. have square pixels. 720x480 comes from hardware designers being cheap and using one crystal to derive both the pixel clock and the NTSC color carrier, the outer edges of that size image are not even visible on most TVs.