Why Amateur fast-scan TV uses the same analog NTSC format as old broadcast television, so it occupies a standard 6 MHz channel: a vestigial-sideband video carrier plus a separate FM audio subcarrier about 4.5 MHz above it. That much bandwidth will not fit in any HF or VHF band segment, which is why fast-scan TV is used on 70 cm and higher. For comparison, FM voice is about 10-15 kHz and SSB voice about 3 kHz, so TV is hundreds of times wider.
Watch out The choice of about 3 MHz is roughly the video portion alone if you forget the guard space and sound subcarrier; more than 10 MHz is wider than any allocated broadcast TV channel.
ATV = a broadcast TV channel = 6 MHz, so it only fits on 70 cm and up.
Fast-scan TV takes a six-pack: 6 MHz. Nothing smaller fits a full moving picture.