alt Hacker NewsRubbish. They don't want to. The tractors have license plates, allowing them to be pursued after the fact, and the NL police have firearms if they want to get spicy.
There have been a number of attacks in Europe of the form "deranged person drives vehicle into crowd". I'm sure the police wouldn't sit back and shrug if that was done with a tractor. The vehicle doesn't have magic properties, the driver has police protection.
The protestors tape their license plates. And I'm happy to report Dutch police generally doesn't draw guns on people who are no direct threat.
And how is the "vehicle driven into crowd" even relevant here? Nobody's using these tractors to kill (intentionally), but they're just many and hard to stop.