Speaking as one who has been devastated by no longer being able to sing (vocal cord cyst that appeared almost overnight, some years back), some of it can be caused by medication side effects and "modern living" pollutants, and foods - that whilst not "junk" - can still cause conditions like LPRD (laryngopharyngeal reflux, sometimes called 'silent reflux').

The difference these tiny lesions can make to the quality and performance of a voice is extraordinary - and extremely depressing.

(a not so) Rich-Joy
Down Under