One explanation I've read is that fluoridation of drinking water plus improved dental hygiene in general has decreased the average number of cavities in the population, driving dentists to pursue other income sources, such as cosmetic procedures (my last dentists was always trying to push Invisilign on me).
New dentist keeps trying to push Invisalign on my family, thinking about switching for that reason alone. Haven't needed braces my whole life and suddenly I'm getting a sales pitch about all the terrible things Invisalign could prevent.
