Clean your cupboards. Mold spores can remain on surfaces for months. Give everything a good wipe-down with some cleaning spray or vinegar solution and then leave the cabinets open to dry out well. And do it again anytime food gets moldy.
Packaged bread should last more than a week, but fresh bread is meant to be eaten within a few days, if not the same day.
I used to live in a desert and bread easily lasted for weeks. Once I moved to what is essentially a rain forest, it doesn’t last more than 5 days. I have to refrigerate it.
Yes, you’re right about the humidity being the biggest factor, and that will also make bread go stale. It also depends on whether it’s prepackaged bread or freshly baked. Prepackaged bread is less likely to arrive with mold spores, and the packaging keeps humidity out during transit and storage. Once it is opened to the humidity, especially in tropical climates, refrigeration will slow any growth.
For people in arid climates, their refrigerator might actually be more humid than their cupboards.
I’m guessing you don’t live somewhere with high heat & humidity, or if you do you run your AC a lot. We keep bread on the counter and in the fridge but not all bread is equally resistant to mold, even some packaged bread. In the winter it’s a lot more forgiving. Also we just open the windows and run fans quite a bit in the summer.