To be honest the large majority of RPi users I have ever met are only adults. Are there a lot of kids who are using it out there?
Students bring their own SD card, since else they are easily misplaced (stolen). This also means boards can be used by any student.
A lot of effort and cost, so we went with the microbit. The kids can easily own them, use a tablet to program them, and for the kids that are older, they can go for the rPi to expand this setup and learn more advanced stuff. By we do not use this as an entry. Kids that do robotics have a better time with them.
So yes, maybe mostly used by adults. The idea of SD cards was a good one. But several flaws held it back; like the non-5v tolerant GPIO. Lost several boards due to misuse... And they ain't cheap if they need to be replaced often.
You dont hear about it as often because for reasons, the kids aren't exactly encouraged to reach out to adults on the internet. Dogs on the internet and all that.
/meant humorously but also seriously serious.
Even if they removed the SD slot, you would still reflash the board over USB. That's how it's done with the Raspberry Pi Compute Module. With some software development it could be even easier than fiddling with SD cards.
In education environments, microSD cards tend to disappear a lot. Having one less moving piece to lose would be a win.