They just wanted a cheap computer for kids to learn on that wouldn’t be the end of the world if they broke it.
I've always said that an old PC (but not too old, because retrocomputing has driven up prices then) is probably the best for that. Can be bought for next to nothing or even free, has extensive compatibility with lots of software, and also decades of detailed documentation.
Ebon's reasoning at the time was that he wanted a standardized computer you could build a curriculum around, that was cheap enough that schools could issue to kids without fear of them breaking it, and which was small enough the kids could take home with them in their backpack. (This was obviously well before Chromebooks and iPads took over the education market.)
Well there is a benefit to using new hardware, No issues with aging caps, no issues with sourcing peripherals (Unless a pandemic comes along messing up everyones supply chains), no issues with compatability.
By only have a single platform to support out the box you are getting rid of having to support multiple hardware configurations which could cause headaches for newcomers on day one. Remember it was basically an attempt to remove the roadblocks of getting people into CS. One of those roadblocks is getting people to "hello world".
IMO its a simailar reason to why Arduino worked so well, sure we could push people to using any other microcontrollers but by having single known board (atleast to start with) everyone is in the same boat and makes it eaiser (and cheaper) to offer support and lowers the barrier of entry imo. Basically is solving the fragmentation issue.
Is it the best way to learn? That depends on how you look at things. IMO it makes it a great stepping stone to get into the field which can then lead on to other things/interests, but you will probally learn more earlier on by skipping the "spoon feeding" stage but that (imo) comes with a steeper learning curve which could drive people away from the subject.
I know I delayed my own learning of the NRF platform to start with simply because at the time the toolchain was a PITA to get started with (esp on an unclean machine that had other compilers installed) so on a number of times I got fed up trying to get to "hello world" I would put it down and come back to it at a later time. However that process of less handholding did teach me more about the toolchain.
I generally agree on the simple, common approach being a great draw for Arduino and its related education. I was going through school around the time when arudino took off. IMO, older vendor toolchains were just painful by comparison. Licensed compilers ($$ license), janky IDEs that were death by 1000 cuts, having to learn different port masks (etc) for initializing different microcontrollers, IO libraries for each microcontroller, proprietary programmers (devices to load compiled software to the microcontroller). IMO, this is where FPGAs are largely still stuck in nowadays.
Though it probably wasn't all that bad. My experiences with the bad side of things largely stems from the PIC lineup. I still have trusted configurations of MPLAB + C Compiler that work vs others I just could never get working. Still have the PIC programmer. Some earlier arm tooling (armv6 era) was quite like this, too. Luckily, it has all opened up quite a bit. Either arudino-level ease of use or even drag and drop. The latter did exist in the armv6 era, since I have a Freescale Kinetis that operates like that, minus the simple IDE & compiler of the arduinos.
Simple IDE also means simple install, operation, and licensing to me. There may be a great paid IDE for the Kinetis, but the moment I have to start juggling more logins, node/floating license files, web-only environments, etc, I just remember it as time wasted on superfluous nonsense.
For me these days I value "Time to hello world" over many other things which is why I would rather use PlatformIO when I'm using a platform & framework it supports even if its lagging slightly behind the latest framework version from the vendor directly.
But looking back, back in the day when we had to walk uphill both ways in the snow to compile and write (get off mah lawn! :-P) I'm grateful I did learn "how the glue was made" instead of just using something ready made. But older grumpier me just wants to get shit done so I'm happy those days are pretty much behind me, but I'm ready to dust them off again if it was really needed.
That isn't something schools can buy several hundred of (with a stable platform) and not worry about electrical testing liability etc. Which is the main intended use case of the Pi.
I've always said that an old PC (but not too old, because retrocomputing has driven up prices then) is probably the best for that. Can be bought for next to nothing or even free, has extensive compatibility with lots of software, and also decades of detailed documentation.