Populism creates problems or do not solve them in order to exist. That's why there is a need to create "the enemy".
That is exactly why people tolerate to-be-dictators like the evil-mustache guy. People needs to be afraid. Populism depends on fearmongering.
This is why people like the evil-mustache German guy was able to work on his platform to have absolute powers.
Why is this unique to Populism? Most forms of power or organizations in general rely on there being a problem to solve.
Not an answer but an appendix. There is common misconceptions on the definition of politics. For the masses politics means to define policies through negotiation and prioritisation. For politicians, it means something related to exert political power.
Using the power definition of politics, it still seems to me that because the ability to exert power is only given when there is a need to be solved, a (for example) plutocrat has a similar incentive not to solve problems as a populist, and would be similarly likely to not be effective. I suppose an explanation that's consistent with both perspectives is that political leaders in general are not effective.
Because sometimes people need to be saved, because the current system is actually broken, unfair, and inordinately stressful.
Populism is the normal population yelling "you forgot about us." Nothing more. Where it goes from there, depends on the politicians grasping that fact, and what they offer as a solution. This is also why populists win - their clientele doesn't feel like they have much to lose; while the competing politician is yelling about abstract global principles and norms and basically saying "your situation is unfortunate, screw you; you don't get it, idiot; pull yourself up, bootstraps!"
Edit for reply: > Populism creates problems or do not solve them in order to exist.
This is just upper class elitism with a thin veneer. Upper classes have constantly, always accused the lower classes of exaggerating their problems; and have constantly, always accused those claiming to address those problems as making them up. It's also a defense mechanism - because it lets you conveniently accuse the lower classes of voting in Mr. Mustache while washing your hands of any responsibility, because the problems were made up and people are gullible, obviously.