They could use a different power connector that doesn't cause this confusion, or they could design Pis to use less power and therefore work properly with more USB power supplies.

A USB connector, at this point, is a PHY (like a serial DB-9 connector), not an inter-ecosystem compatibility promise (like a FireWire or SCSI port.) Lots of things use USB for lots of different incompatible use-cases. They just happen to share a connector.

But on the other hand, you can also think of it like a regular PSU: all motherboards connect to all PSUs, and there’s no way for a PSU and motherboard to communicate to “lock out” a mismatch. And a PSU will seem to work for a given configuration of motherboard+CPU+peripherals, until you drive that configuration hard enough to overdrive the PSU, and it shuts off.

The solution in both cases is the same: you overbuy on PSUs. A good high-wattage-rated power supply (whether a USB one or a desktop molex one) will power anything below that wattage requirement just fine. USB PSUs do negotiate power draw with the client device, so you can run a Pi off a big-brick laptop-class USB charger without damaging it.

And that’s mostly why Raspberry uses USB power, I think: if you already have a big beefy USB PSU from something else (as most early-market adopters do), you can use it to power your Pi for playing around, without having to buy the Pi its own PSU, if you’re not sure you want/need to set it up for its own standalone use-case.

(Also, the Pi will run just fine on a wimpy 5V1A iPhone charger if you don’t tax it very hard. Just like a cheap desktop PSU will power a gaming rig with a beefy GPU, if you never open a game. And most embedded use cases, e.g. PiHole, don’t tax the Pi very hard. So there’s a lot of cases where people get along just fine with the cheapest possible configuration, where forcing them to buy an actual power adapter would make things a lot more expensive for no gain.)

> or they could design Pis to use less power

You know that they stop selling old-model Pi’s, right? It’s not because they want to. It’s because those chips stop being manufactured upstream; and Raspberry doesn’t do enough volume to drive production of SoCs all on their own.

Raspberry is constrained by what parts they can put in a Pi that are both available and sufficient for the use-cases their customers have (e.g. driving monitors at native resolution.) Those chips have minimum power requirements. The power requirements never go down, because there’s no high-volume customer with exactly Raspberry’s use-case (where that use-case is “using process-shrinks to build a graphical desktop SoC of the same performance at ever-lower current draw, rather than achieving ever-higher performance at the same current draw.” An SoC process-shrink that is taken as-is with no commensurate re-layout for increased perf, is extremely rare in the industry. Not rare in microcontrollers, but an MCU can’t drive a desktop computer.)

You might suggest they undervolt the newer chips — and they do! — but there’s only so far you can undervolt a chip before it just stops functioning at all. (Especially an SoC, that contains DRAM that must get refreshed, IO controllers that must drive peripheral lines with to-spec line voltage, etc.)

I'm just nitpicking your otherwise great post here but wouldn't the IO voltages be entirely separate from the core voltage? Or do they all need to be kept within a certain range of each other?

Is it such a terrible "learning" Experience that yanking the power cable out is a bad idea as others have said the pi's should have better power supplies.