No, why would it? ARM is well-known, well-supported by the software ecosystem and there are tons of cheap chips readily available so you can pick whatever you like.

RISC-V has none of these things right now. One type of chip available, I doubt they could have gotten it at the time (or even right now) in the numbers they need, it would need companion chips for things the current one has integrated (Bluetooth), would be more expensive and would likely require more software work. Exciting, yes, but at the lower levels "boring" is exactly what you want for a project like this. The entire thing is supposed to be cheap so you can distribute it widely and additional effort spent has a way higher impact if it goes to documentation, teaching materials, example projects, … than to making low-level changes most users won't even notice.

Can you buy a RISC-V device off the shelf with integrated Bluetooth?

It looks like BT was the architecture driver, so they used https://www.nordicsemi.com/eng/Products/Bluetooth-low-energy... - the radio is the difficult bit, and the processor having spare capacity is a convenient by product.

There is a very long history regarding the BBC and ARM, you could say that without the BBC ARM would not have existed at all.

RISC-V is the new Rust

Not yet. But hopefully soon.