It's a deliberate choice by companies because they sell you the thing, and the service to fix the thing.

There's a lot you can still do. All the suspension, battery cooler pump, brakes, wheel bearings, a ton of things to do with the electrical system and lights, fuses and relays, window and lock motors, blinker arms and switches, fluid changes, hvac and ac components, the traction motors themselves....generally the only thing hard for a shade tree mechanic is the battery itself. They're really heavy and hard to remove.

Now some components are going to be hard to get a hold of because there isn't any third party companies making replacements, but eventually as need arises, they'll get made. Until then there's places like pick n pull where you can go take used parts off used vehicles or buy used and tested components from ebay if the manufacturer won't sell you something. I bought a new oem hybrid battery just a couple years ago from a Toyota dealership and installed it myself.

Eh....that's still pretty doable. Many things actually got easier for auto work. A $12 bluetooth obdII dongle and a $4 piece of software on your phone will give you most all the trouble codes you need to diagnose problems, and that's it it doesn't outright tell you the issue. Almost no car parts are parts paired and thanks to the internet there's guides that are way better than a Haines manual to show you how to fix things, as well as a dozen different places to order parts from.

In the past 15 years the only time I've used a mechanic was to replace a clutch.