1 - It does not imply that much work. Not even close. For instance, my uncle and aunt rented a flat for 6 years to the same family, and in that time my uncle had to go there about 1-2 times for minor problems, and I don't think it's an exception. There is a bit of work at the time of finding new tenants, but in the case of the people I know, it's like an average of 4 hours of work a year at the very, very most.

2 - (and most importantly): middle class people who invest in real estate are keen on having a rent. Stocks don't necessarily give you that. They see buying a house and renting it out as a way of having a monthly recurrent source of income.