At risk of stating the obvious, the concentration of effort has been on reducing the risk of cargo fire, or containing its effects. Hence the dangerous goods regulations, and training for Customer Services, and rules on what passengers carry. That's the main defence.
Once you actually have an uncontained cargo fire - as with an uncontained engine failure and fire which can damage the wing structure, or uncontained fire in the cabin - you do have limited time available. It's for situations like this that captains are paid their salary. Fortunately, the frequency with which it happens is about the same, to the best of my knowledge - of the order of no more than one every decade, at a guess?
Whilst we might all say that safety has no price, the fact is that all risk analysis has a cost dimension. Perhaps in some circumstances cameras in the hold would help - as they might directed at the engines and in the cabin. However, until the benefit (perhaps one accident in six or seven years) outweighs the cost (? £10000 per aircraft, plus the cost of reengineering pilot procedures), it won't happen. Bear in mind that the cost would have to be passed on ultimately to the people paying for the aircraft to operate - freight shippers and passengers. Don't blame the airlines - ultimately, what price are the fare-payers prepared to pay for safety?