We use our credit union debit cards to get cash at cajero automaticos in Mexico. When we get our statement it says "fee waived due to RBP". I asked our credit union what this means and they explained in terms only a banker can understand. Anyway, for whatever reasons we do not pay to use ATMs in Mexico most of the time.
The fees are set by whoever owns the machine and they can charge whatever they want. Which is why we only use machines at banks. Actually quite a few reasons for using machines at banks - better rate - usually safe - if a problem we can go in the bank - I think there are more reasons.
Many places we go do not have the ability to accept credit cards. Tianguis would be an example of mostly cash businesses. Small town stores may not take credit cards. Carrying a lot of cash is not our favorite thing to do but sometimes there are no options. We do not carry much cash on our person but we do have hiding places in our vehicles.