Why people are gullible doesn’t just have one simple explanation but I believe the answer rests mostly on the idea that many of them want black and white solutions. They want to be led by someone else and told what to do.
Religious cults wouldn't exist otherwise.
In the US the Trump base would jump off the nearest cliff if told to by their leader which is frustrating for many of us. They will repeatedly vote against their own intetests because a simple message full of empty promises sounds better to them than reality.
Democracy is naturally messy as is life and not everyone gets what they want. However, when it works the most people possible gain benefits from its structure. In other words, there is some form of collective winning however imperfect. This means no one gets everything they want but at least most of the basics are covered through some shared discomfort.
Gullible people very much like simplicity which is why Trumpism was so appealing to them. They heard the grocery list of promises without reflecting on whether all of it was even possible.
These are grown adults we are talking about.
It is hard to feel sorry for MAGA voters once they wake from their stupor only after having been personally affected because you just know that they would do it all again in a heartbeat when the next used car salesman comes along.