Because a custom UAV isn't going to get taken out by a microwave beam weapon or an attempt to spoof GPS, or an attempt to gain root control. It will shrug all that stuff off and just keep flying to it's destination.
The question is whether or not you want to lose for 5K, or win for 10K. Considering they might be carrying a million dollars worth of drugs, I would think it would be in their best interest to neutralize these methods of capturing drones.
The drugs didn't cost them millions to produce. That's the estimated street value.
A hardened drone can't be built for $10k and I challenge you to prove it can.
From: US Border Patrol Drones Hacked by Drug Cartels
The drug cartels are hacking US Border Patrol drones in order to cross the US-Mexican border illegally.
It has been reported by the US Department of Homeland Security (DHS) and the US Customs and Border Protection (CBP) agency that drug traffickers have hacked their UAVs to cross the US-Mexican border illegally.
UAVs (unmanned air vehicles) are being used by the US military quite extensively already and now these are in use by the other US law enforcement agencies such as border patrol and local police.
However, the difference is that the military owned drones are quite expensive and worth millions of dollars whereas the drones used by law enforcement and local agencies are smaller and less expensive. Understandably, the smaller drones arent as effective in evading hack attacks.
That is because to minimize their cost, various standard drone modules need to be deleted including the one that ensures the security of the drone in the case of GPS spoofing, which is a trivial cyber-attack.