Safety?
Hatzerim
It's not only money, where's the safety having a 'loadie' sitting about waiting for something to happen. He sure isn't needed to load or unload the a/c. Even if the cargo did catch fire if it were containerised he'd have a hard job even getting a probe anywhere near the source, and how would he know where the source is? Some years ago BA were forced to stop flying the 747 combi as the UKCAA insisted that if the cargo was mixed with pax on the main deck then a fireman (not a pretend fireman) was positioned on the pax side of the bulkhead in full fire gear for the duration of the flight. Now that's safety-and the airline decided double quick time that it wasn't worth the hassle.
You have to be proportional in all of this. How many fires per thousand hours etc etc. I'm no actuary, those people are paid far more than pilots to figure out the risk v profit.
S