According to scientists from the the U.S. Centers for Disease Control and Prevention, decades of people using treatments but stopping short of completely killing the fungus meant the remaining fungus learnt how to survive. That made the treatment useless the next time around as the fungus mutated into a stronger kind of fungus. The meds you took by now, just like antibiotics, ended up creating stronger, mutated fungi. This led to antifungal resistance, which makes it almost impossible to get rid of fungus.