The FAA does however have a parallel track, called Experimental-Amateur Built (E-AB) where if you build the airplane yourself for educational or recreational purposes, it’s subject to a mostly separate set of rules. They are generally more relaxed in terms of what maintenance and modifications you can do but stricter in terms of what you can do while flying (can’t take passengers for hire, for example). Most pilots prefer the certified/safety-first/highly regulated track, but the government recognizes it’s a trade-off and offers the other option for those who prefer a more DIY-friendly world.
Not saying this would necessarily work for medical devices, but there is precedent for acknowledging the trade-offs when it comes to DIYing safety-critical stuff.
Prior to this pump + Dexcom, he had a Medtronic 530g + glucose monitor. It was not internet connected out of the box, it required a $100 gadget that would transmit his blood sugar to his cell phone and then to medtronic's awful website. Fortunately folks developed Nightscout to scrape Medtronic's website and provide a much better experience. With Dexcom being a much more modern option (the CGM transmitter has built-in bluetooth) - we don't really need Nightscout, but it's convenient for me to watch his sugar on my 2nd monitor when he's at school (he's only 7.)
The problem is not in my opinion regulatory processes or clinical testing. It's been simply a lack of urgency/competition. Beta Bionics has started to make Medtronic and other competitors step up their game in recent years. https://www.betabionics.com/