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.