Amazon is reliable, sure, but what do they have - 99.9% fulfillment, 99% on time, 99% with authentic products, 97% of listed products in stock? Those are guesses, but apply those numbers to delivering vital daily medicines and the problem becomes pretty obvious.
Keeping in-stock rates high and "on time with authentic products" rates near 100% is not an easy task. It's not something pharmacies do perfectly either, but their shortages are generally at a store level rather than national, and they're not asking people to completely switch delivery mechanism to trust a space with online one provider.
Another guess is that changing habits(especially since buying drugs is an infrequent event, and that we're dealing with seniors) and creating trust we're other reasons.
But the main issue with drug delivery is the need for reliability; you can't have somebody's heart medication ship out late or get lost in transit, basically ever. And if you change offerings or go out of stock on specific products (which most retailers do often), you'll quickly be seen as an unreliable way to get any kind of regular medication.
Plus, you can't let any fakes or low-quality products into your supply chain - so sourcing new suppliers is hard, but running out of suppliers for any single product is a crisis.
So being an online seller for use-as-needed prescription meds might be easy, but the bulk of the money is in people taking drugs daily, and that stuff is damned hard to offer.
Basically, the largest potential market for you is not tech savvy at all and makes it hard to convert.
I think there’s a big opportunity for insurers to pick a default mail pharmacy that customers out of. So depending on your insurer, the EMR automatically files with a pharmacy you don’t care about and mails it to you within 24 hours.
My doctor sends short term stuff to a local pharmacy for me to pick up, and my daily long term pills to Optum, who charges my CC and mails them to me. They take about a week to arrive, but you can set it up so they automatically recur, so you always get your next 90 days before your current pills run out.
Looks like it’s already happening, albeit in an opposite direction, with Aetna acquisition by CVS.