Agapanthus are actually not bulbs, they are rhizomatous plants. If its any consolation, our amaryllis never lose all their foliage either. Maybe we just live a charmed life. There are different types of agapanthus. Some are 100% deciduous even in warm climates (most of these are from a group called the Headbourne Hybrids), some are semi-deciduous and some are evergreen. It depends on the species you have planted, and the different cultivars within the species.
I have exclusively planted "Elaine", which is a 100% evergreen agapanthus, on my property because I like its deep deep dark color better than any other agapanthus. The lighter varieties appear washed out to me and I don't like white flowers. Another nice evergreen selection is "Ellamae".
You must have a deciduous or semi deciduous variety planted at your place.
Doesn't mean you are confused or "not that smart", just means maybe you didn't research before you planted or maybe got a generic type.
Some agapanthus are hardy and evergreen to 20F and slightly below. Many survive well to zone SEVEN. Mine are evergreen, because I made certain I was getting an evergreen variety as I did not want any bare spots in winter where they grow. Yours apparently are not an evergreen variety.