The companies do this simply because this is the way to grow their market. For every single person who finds enjoyment in twiddling with their tools, there are hundreds who just want the thing to work and get on with other things in their life.
Yes, there are economies of scale that come from chasing the middle, and yes, it's probably easier to just mimic an iPhone than to do the creative work to try to invent something better than what worked before. And yes, the tradeoffs, design goals, economic targets, and principles of repairability and customizability that go into, say, an F150 make those pretty popular trucks, but since Ford is still making F150s, and Chevy, and Dodge, and Toyota also have offerings that are direct competitors in that space, that doesn't mean that a hypothetical competitor can maximize their market share by making yet another F150.
Why does everything cluster into the same choices?
i suspect it's the same reason you get a cluster of the same stores/shops in a region.
It's the classic economic dilemma - Hotelling's law (https://en.wikipedia.org/wiki/Hotelling%27s_law)
The market doesn't know what it wants until the options exist. Until a culture forms.
Almost all companies are competing in one direction only, a race to the bottom. There's sometimes some semi-geeks freedoms offered, but usually those are gilded cages too. We'd have to go back some something like Maemo to see consumers getting something actually empowering, a portable mobile Linux+FreeDesktop offering.
Just like how most of us treat cars and stovetops as appliances?
Look, becoming omnipotent is an admirable pursuit, but time is a finite resource and by fuck most of us simply do not have enough of it. We can choose to become potent in something and most of us are in fact potent at something, but that isn't necessarily going to be electronics or computer programming.
hardly anyone would be tinkering their phone to make the hardware do more than the default applications.
The same is happening (or is already happened) to cars.