The developers are used to Java, and as someone who's worked with both Java and C++, Java is simply better for the kind of iterative development minecraft seems to do. From what I've seen (which admittedly isn't much more than the public facing history and the minecraft live/minecon events), there isn't really a strict roadmap and they seem to value messing with features a lot. Also, the game was only rewritten in C++ to support multiplatform ports, and bedrock isn't even the first time they did it (though, the other C++ versions, also known as legacy console, weren't handled in house). The existence of a windows version is a strange curiosity stemming from the microsoft buyout and their ability to do so since that codebase is insanely portable.

Also, mojang (not microsoft) really appreciates modders, which java edition is strictly superior for