Soot builds up in 2 ways, low idle speed, and working it HARD where a lot of fuel is used to maintain RPM. If you are running at high RPM with little load, such as towing a ground driven rake, then you can go a very long time before a regen is needed. If you are tilling or hogging thick weeds and really working the engine where you can hear it burning more fuel, then you will have shorter regen cycles.
Not much different than road trucks on the Interstate. If towing a trailer, then a regen happens more frequently than if just tooling down the highway empty.
Idling soots up the DPF quickly, so avoid idle time as much as possible.
When running at optimum levels, high RPM with a lean mixture, there is less actual soot, and the DPF gets hot enough so soot doesn't accumulate, but as you dump more fuel in for working to keep the RPM up, then the exhaust coming out of the cylinder is heavily sooted and that sticks well because there is also more unburned fuel in there as well.
Also keep in mind that there is no DEF to help catalyze the exhaust, only the DPF to capture soot.