It's probably part of the initial franchise standards, required and signed off by the fast food corporation. Or the shopping center design. We know as a society, that we need garbage cans, so they are budgeted for and installed.

But owners are always looking for ways to save money. If the garbage can works fine, it gets maintained. But if it gets hit by a car, or the wind blows it away, it might not be at the top of the list of things to fix. The remnants of the garbage can are removed. The expense gets put off for another month. And slowly the lack of garbage cans becomes normal, and staff can remove another responsibility from their list.

Now the situation becomes, who wants to spend a bunch of money to put in garbage cans, and also add onto the staff's workload? It's not like customers are asking for the manager to install garbage cans.