Why is sludge formed in some car engine oil ? Due to the oil or due to the engine? How can it be prevented?

I have never experienced that the sludge formed in my cars engine oils. But I have heard and read about it quite a lot that it happened even to the expensive cars.Why is sludge formed in some car engine oil ? Due to the oil or due to the engine? How can it be prevented?
Some dust slips by your air filter, and past the engine rings and goes into the oil. Plus a little moister from the air. Impurities in the gas slip past the rings and down into the oil pan. Plus metal particles from wear. Carbon builds up in the combustion chamber, and bits go past the rings and into the oil. Oil can break down after time and add to these deposits. This is how you get sludge. Change your oil and filter every 3 thousand miles and you will avoid these problems.Why is sludge formed in some car engine oil ? Due to the oil or due to the engine? How can it be prevented?
It's just what happens when you heat and then cool the oil over and over. That's why you must change your oil, is because when this happens the oil eventually starts to loose its lubricating properties. Just make sure to change your oil as often as you should. And if you want to spend extra money for a better oil, but Full Synthetic.
KensofAz is correct its blow by causing gas to go past the piston rings and into the oil contaminating it acids