The operators c, d, and y expect a motion, like w, e, etc. The second character in the following pairs is not a motion so it is a NOP and nothing is overridden if we use them in mappings.
cd cm co cp cq cr cs cu cx cy cz
dc dm dq dr ds du dx dy dz
yc yd ym yo yp yq yr ys yu yx yz
v is not an operator but it has similar semantics. There are fewer available pairs, though, because it is possible to use an operator right after v.
vm vo vq vv vz
Vi didn't have anything assigned to g so Vim kind of treated the namespace as a dumpster for new two-characters commands. Here are the pairs that are left:
gb gc gl gs gy
z was free, too, and it got the same treatment, with an even worse outcome:
zq
[WIP]
ZA ZB ZC ZD ZE ZF ZG ZH ZI ZJ ZK ZL ZM ZN ZO ZP ZR ZS ZT ZU ZV ZW ZX ZY
[WIP]
@jchros all good points.