There's an extended release version of Adderall, but also even instant release Adderall is still quite common to prescribe. Compared to other psychiatric drugs discovered in the same time frame, Adderall is remarkably effective, and I think this is reflected in the relatively small amount of research that has subsequently gone into ADHD treatment. There's also of course a market of people looking for Adderall IR prescription to help them study or work.

I can only really speak to what I've seen working at a hospital in the northeast US, but it seems that as of 2018 amphetamine was the most prescribed drug type for ADHD across the country, and actually going up: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6261411/#!po=21...