Most cargo planes are expected to run out of civilian airports where a failure could result in debris launching themselves into populated vehicles or buildings. In contrast a crop duster launching off a dirt runway and expected to go no more faster than highway speeds actually can be built fairly loose, and often are. For example, this duster here [1] won a award in the 70s for innovations like a "pressurized cockpit" and "air conditioning".

[1]https://en.m.wikipedia.org/wiki/Grumman_Ag_Cat