Firstly, there are all sorts of biases involved. We're far more likely to hear about situations like these, than native development of solutions.

Secondly, there is a non-trivial cost to thinking up ideas and experimenting. Beyond costing time and resources that the farmers may not have/may not want to spend, experimenting as a whole is pretty risking. Being an outside player with far greater ability to take on risk has an obvious advantage.

Thirdly, while the farmers probably don't want to fight elephants, in the scheme of things, they probably individually rate the well being of elephants lower than their survival. We on the other hand probably rate the importance of the two far more equally, and thus have a greater incentive to solve the problem in such a way.