It's less that it's simple (it doesn't really seem simpler to me than any other fundamental approaches to macro, no?) than that at least real-world behavior of governments, and changes in the world as a result of that behavior, doesn't all seem to point strongly in the direction of something about it being wrong or badly incomplete. It's simple like universal gravitation is simpler than epicycles.

Ok and the fact remains, that the vast majority of experts in the field dismiss MMT as something that doesn't provide much of value to the field.

Thats the important part here. Whatever your opinion is on any of this, basically all the actual people who know what they are talking about, disagree and think that MMT is basically valueless.

The world isn't that complicated. Its brutal and uncaring. We make up complicated systems beacuse we'd rather not face the pointless brutality of it all. Contrast the complexity of religious faith in life after death to the biological reality on the ground for the best example of this.