Why do hidradenitis constantly reoccur?

Depends. You are predisposed usually due to the way your sweat glands are put together, it often happens in other family members. Sometimes it is due to weight, hygeine, weather, type of occupation, and other factors. You should have general physical to make sure not thyroid, sugar, or other medical condition, consider suppressive antibiotic like Doxycycline if recurs often.
Hidradenitis Rx. Hidradenitis is a poorly understood inflammatory and infectious condition of the apocrine skin. If courses of antibiotics or local steroid injections are failing to control symptoms, you may want to pursue definitive treatment, which would be plastic surgery to remove the apocrine skin. While invasive, this can cure the problem and should be covered by most insurances.