The reason for the incompatibility is that. Well the eight
Pin version separated the Color and brightness signals
Which funnily enough Is coincidentally is pretty much the same as the S-Video standard albeit using RCA connectors.
The Five pin version is rarer as only the earliest model Commodore 64 "Bread bins" have five pins.
(not entirely sure why Commodore changed the number of pins though)
I'd suggest checking out The "8 bit guy"s Commodore history part three on YouTube for a more complete explanation.