Later, Mojang hired 4J to make the console versions. Java on consoles was a bad combination, so they started writing their ports fresh from C++, but heavily derived from the Java upstream as point of reference.
Meanwhile, Mojang was developing their own, separate C++ rewrite in house for the pocket edition. This “Bedrock” edition later expanded into the Windows 10 edition, caught up to Java for almost all functionality, and around Update Aquatic replaced the old 4J version on consoles.
This particular project is a decompilation of the discontinued 4J line.
As to why Bedrock / PE beat 4J, it’s not completely clear, but there is some well founded speculation. Most likely, when pocket edition was started and 4J was hired (~2011), the idea phones and consoles could run the same version was far away, Mojang didn’t want to worry about consoles, and may not have believed feature parity between platforms to be possible. As phones became more powerful, and as the pocket edition became feature complete after over half a decade, Microsoft decided they only needed one. A shame really because 4J’s version was, in some ways, still a better console experience.