You've left out a few things the landlord does and the risks they assume (at least here in the USA, I'm not sure about Paris):
- mortgage costs
- property taxes
- insurance
- utilities
- repairs
- maintenance
- savings for large future capital outlays (new roof, furnace, etc)
- renters not paying
- empty rental units
- loss of investment opportunities of the capital locked up in the building
- possible loss of all income due to fire, etc
- 34 other things I'll leave out
It may look like landlords have it easy but as a former commercial landlord I can tell you it is not easy at all.