> It's absolutely crazy that a game so popular - let alone any game - was originally written in Java.

It did not start being popular :)

Seriously though, I think Java helped it get so much traction initially. Writing mods was tedious but not that difficult, and it was multi-platform for free. Nowadays I assume the vast majority are playing bedrock on consoles or PC, but at the beginning it was rather nerdy and being playable on Linux and Mac was nice for some tech-minded people.