I believe the correct answer is "What is, all the time".
Eh', I mostly beach hunt but in the off-season I go to parks, soccer fields and playgrounds. My average for a park/playground is less than $0.50/hr. I might score one piece of junk jewelry every 16-20 hours and a piece of good stuff every 400-500 hours.
Its not the equipment, heck, I've owned some of the most expensive detectors made. Its not necessarily the operator as many of have mastered swing techniques and the machines controls. The reality is you can't find something that isn't there. And when a good target is lost, you have to find it before your competition.
Being in Florida, we have scores of folks that hunt day and night. Then we have snow birds that come down and stay half the year. On top of it, we have tourists that flock to our locations. Worse yet, there are TV shows and social media that increase the hobby awareness by hundreds of new folks every month.
After you've mastered your machine, the key is diligence and persistence.
H/H and G/L! -David