Frustration at an imperfect democracy where "no one listens to me" - and then that's turned outward and manipulated just enough by rightwong interests (who have a tailwind, with corporations and Capitalism often leaning right in function and lobbying).
Voters think this is an easier way to get attention than actually participating, and some of these voters will be voting this way to "scare the major parties" who they consider out of touch/corrupt (hence the whole system is broken).
...and some of the major parties being out of touch is because class consciousness only extends so far. Wealthy politicians can't realistically understand how difficult and inconvenient life is becoming for a lot of people.
Most people just want to see public services be improved, and better laws against scams and unfairness. Zoran Mamdani is right.