If they took any sort of money from their business, it would be taxed as income. But if the money just stays inside the business and is used to buy more rental buildings-- what's there to tax? So the business keeps growing and growing.

Case A: the owners take a paycheck of $100,000. It gets taxed at 30%, they get $70k.

Case B: the owners take no paycheck but instead buy a $100,000 property through the business with the business's earnings. They pay no tax but now own a $100,000 property which will now augment the business's earnings further. Down the road years later, they finally take a paycheck at $300,000, which is taxed down to like $180,000 or something. Still more than 2.5x the Case A payout, and let's not forget they own that much more property now on top of everything else.