Which is easier, decompiling Minecraft Java using the MCP or decompiling and making the same kinds of changes to the Minecraft Bedrock version? And would the answer to this question be significant towards a reluctance on the part of Mojang to include Java in the Better Together update?
Decompiling the Java edition is over 9000 times easier.
And yes, that is very significant; Microsoft want more control over things, so they can charge for add-ons, servers, etc.
Making the Java version crossplay would be rather difficult. For one, the Java version is the only edition that's coded in a different language from the other versions, and secondly the two platforms still have different features. Probably not worth development time trying to resolve headaches, especially since the Jave Edition is the least bought version of the game and isn't what they consider the primary version anymore.
Yep, Microsoft is demanding that over 20 million people upgrade to Windows 10, or they're no longer relevant. Because they'll make more cash that way, and don't care about the core community that made the game so popular in the first place.
The Meaning of Life, the Universe, and Everything.
Yes, you get a free code for the Windows 10 Edition with the java edition. For now.
That doesn't help with Linux or Mac, or anyone with an older computer, but... *shrug* - it's Microsoft; they want everyone to use THEIR system, to spend money on their upgrades, and use the platform where they can control the micropayments - for servers, "mods" (well, add-ons), skins, maps, etc.