There is an entire product category of "universal power adapters"[1] that wouldn't exist if GP's problem weren't an issue - and that was back when most adapters were just "dumb" power sources that provided a fixed voltage with fixed maximum current.
There is no way to combine Micro USB, USBC, Thunderbolt and whatever Microsoft was doing with Surface devices into one adapter without separate electronics for each port.
> 1) Companies are not incentivized to produce incompatible cables
They absolutely are. I figure, it's not even greed (most of the adapters were included with the devices) but simply "designer convenience". It's certainly easier to design a device if you can choose an arbitrary input voltage and max power for your device.
It'll also certainly make your life as a manufacturer easier if you only have to provide warranty for devices that are run with your own power adapter.
Also, Apple in particular seems to have an aversion to follow any kind of standard not set by themselves if they can in any way avoid it. See Lightning, Thunderbolt, MagSafe, etc.
Doesn't mean this is better for anyone else except from the manufacturer.
> 2.) Would the amount of charging cables you have purchased in your lifetime even fill up one regular-sized (13 gallon-ish) trash bag?
I haven't measured but this isn't the point for me. But it used to be that the amount of adapters that you had to take with you were increasing: I.e. if laptop, phone and ipod all had different adapers and you were travelling, you had to take three of them with you.
> All my consumer electronics devices have stopped needing their own charger for years now.
Yes, so have mine, thanks to the EU regulation.
[1] https://www.kaufland.de/product/440138880/