It comes from the history of physics. A few equations define classical dynamics. Maxwell's four equations describe electromagnetism. A few short equations define quantum electrodynamics. High-energy physicists have been looking for something equally terse. It just isn't happening.
I'm sure whatever turns up for quantum gravity will be hideous to begin with, but then eventually we'll understand it.
You're also confusing understanding with logical omniscience and omnipotence. I know all the rules of chess, but I do not know every fact those rules entail, and I do not know how to win every chess game. Even if I did know those things, certain moves are impossible even though I know everything about chess.
This is called the hierarchy problem. https://en.wikipedia.org/wiki/Hierarchy_problem#The_Higgs_ma...
Knowing fundamental principles wouldn't make us all powerful.
Very interesting argument though.
I just don't dig the obsession with "aesthetics". It just doesn't compute. I understand the need for simplicity, but there's JUST NO PLACE for aesthetics in science. We need simple verifiable experiments and results, no "my model is more beautiful than yours" stupidity.
One important thing: scientists need to recognize where science ends and passion/preference begins. Scientism is the greatest foe of science.
Disclaimer: I'm not a scientist.