1) Lazy: don't want to fix things, paint walls, touch up your bath tubs. Don't know anything about caulking.
Basically, they think of a house just like a stock certification. These people may not last long in real estate.
2) Impatient. They can't put up with the prospect of waiting for a long time before harvesting. This could be a mulitple year period. They are not prepared for the prospect of zero real income or even small loss while holding the properties.
3) Don't want to be a landlord, collecting rent, going to court to evict. Thinking of landlording as extreme pressure. Any small issues came up, they would sweat or get sleepless in the evening.

I tell you. Real estate is hard. Harder than playing in stock market. Even if you understand the power of leveraging and "cash-on-cash" return, you still may not have the right mindset to endure this business.