Say you have $100,000.

You could buy a house worth $500,000 with 20% down and a 30 year note. As long as you pay the mortgage, it doesn't matter how much the market value of the property changes. A drop of 40% in real estate prices that lasts for five years is not necessarily a problem.

On the other hand, imagine you put $100,000 into a brokerage account and were able to get 2:1 leverage. You could then borrow $100,000 and buy $200,000 of stock.

However, if the market runs into a bad patch and that stock decreases in value to $120,000, your equity is now only ~16.7%. This is below the minimum margin requirement (25%) for your account. Your brokerage calls you up and says you need to put an additional $10,000 in your account - that's a margin call.

If you don't have the $10,000 then your brokerage will sell enough of your position to bring your account back within requirements; possibly at the bottom of the market.

Real estate: 5:1 leverage, no margin call Margin account: 2:1 leverage, plus margin calls

You can get around this by purchasing leveraged funds/etc. Although that should never be considered functionally the same. That said, you could consider real-estate interest+taxes+upkeep similar to the inherent loss/overhead in leveraged funds.

The lender can't foreclose if the house loses value. You have to stop making payments before they are allowed to take the collateral.

In contrast, if you buy stocks on margin, they will forcibly sell your position if the value of the collateral gets anywhere near the loan value.