Cobalt 60 with a half-life of 5 years=annihilation

The nastiness of nuclear war. The cobalt bomb was never made but the thermonuclear device would seed the landscape with radioactive cobalt 60 that would hang around for a little over 5 years. A few of these would certainly complicate life and worse yet destroy all life. Was it reason or economics that curtailed its production?

Cobalt bomb [Wikipedia]

The Never-Tested Doomsday Bomb