In my parent's day, and my younger days, almost every politican had had a life first. Lawyer, doctor, surgeon, Special Forces, union official, plenty of WW2 service too, you name it. You may not agree with their policy, but there was usually a huge breadth of life-experience, and often demonstrated knowledge even if you vary on the conclusion. We generally had older politicians as they had experience. There was a remnant of the once popular idea that after a successful life you gave something back in politics - locally or nationally. Now there's an expectation politicians need to be younger, media friendly etc.
So now we're overrun by professional politicans who get their degree in PPE and expect to start chasing power the moment they graduate, with little more than family wealth or the increasingly common short PR/media career to look back on. They can draw on short political experience and little else. They increasingly have no idea how the world works.
No amount of advisers and civil servants can close that gap.