Drug smuggling continues to exist because drug smuggling is wholesale and FedEx is retail. And FedEx wouldn't know to provide security to prevent competing dealers from holding up their drivers.

I suspect that package services are used with high frequency by criminals without these constraints, e.g. the ones committing mail fraud. The police deal with this not by searching the contents of random packages but by arresting the actual perpetrators regardless of what they use for a delivery service.

There seems to be a common impression that if the police can't find you using one specific investigative method then they have to give up and go home. There are hundreds of different ways to catch criminals. Most of the ones people complain about the police losing are ones they never traditionally had to begin with.