Speaking of the guys who watch the car in the street. We also see this in many parking lots of places like grocery stores. They serve a number of functions - they will help you find a parking space - they will stop traffic and help you park - they will watch your vehicle - they will help you load your stuff - they will help you back out of your space etc. - they also take care of the lot by picking up litter - they sometimes have cardboard to put on your windshield to keep the sun out while you shop - some will wash your car. These people live on tips. They created a business for themselves. We watch and see that Mexicans do tip them so we tip them. They do not make much and do not expect much. But their purpose is to be there to help you. They do not mean to hassle you. Their intent is to provide a service.
This also applies to the kids who bag groceries - they are not paid - they bag for tips.
The list of services people in Mexico might provide that you will not see in other places can be long as the people see a need and they find a way to fill the need. They are more than willing to work to help you for a small compensation.
Many years ago my Aunt told me the little old lady street beggars have no other means of income or social security or whatever so the Mexicans with money give alms to the poor. Now some say this has become a business with people finding the little old ladies out in the country and bring them into town to beg. Then the ones who brought them take their money. We do not know if this is true. We still give the old ladies something if we have something. My Aunt used to give 10 centavos - now we give a peso. No one will get rich - and we will not go broke. If we see a Mexican give them money then we give them money too.