Why is the populist party generally regarded as a failure by historians?

Populist parties are usually regarded as failures, because they only emphasize with the public in the short run and not in the long run and promise fake proposals, which would almost be impossible to carry out. A populist party is often made to appeal to people's hopes and fears, but if elected, would not necessarily carry anything out to appease these ideas.

Not sure this is a hard one huh