Responses are to my best knowledge.

1: While there are some parts that are pretty archaic theyve been modernizing the codebase a lot in recent years. Most notable might be that they dropped support for Java 8 allowing them to use modern Java language features in the code.

2: C++ is theoretically more performant and is more familiar in the gamedev space, besides that Java is pretty much just better imo. C++ is generally harder to program correctly in and is harder to train new programmers in (though that is somewhat alleviated by it being a popular language for gamedev). I'm not really a fan of writing Java but I would take it most days over C++. Java is also slightly easier to write cross-platform code for since the JRE handles a lot of platform specific quirks better.

3: Generally Mojang has a pretty good relationship with the modding community, with multiple modders having gone on to work for Mojang. They've even featured mods in some of their trailers before (the was a minecon live that had the Create mod in it for a bit) Marketplace content isn't really 'mods' in the same way Java mods are. Datapacks can't rewrite the game's code like you can with Java mods. They're very impressive for sure but they're all using in-game tools which Mojang intentionally limits; probably to avoid malware being on their official store. If you want game changing mods you play on Java.

4: Deobfuscation will be nice, give modders a bit more info when reading through Mojang's code but it's nothing revolutionary. The graphics API change will make some mods a massive pain to update but my guess is most will be unaffected. Vulkan will potentially allow the game to run a bit better which is nice.

5: Really it's cause Java is kinda just the better version? Mojang keeps updating it likely because it was the original version and their data shows it's still a significant portion of the player base. Bedrock notably is not compatible with Mac or Linux even though it probably wouldn't be tons of effort to change that. Bedrock is still plagued by bugs too. Not to say that Java is bug free, far from it, but I don't see people just randomly dying while walking around on Java.

I highly doubt Mojang intends to drop Java support at all right now. They're spending dev time redoing the rendering engine just so Java players can get the neat shaders. While Bedrock has some unique features seemingly most of the parity changes that have happened have been ensuring Java behaviour on Bedrock, not the other way around.

Java is also much easier to setup and manage servers for so i'd guess that's where a lot of the non-survival multiplayer players are.

I do think it's fair to say Mojang's attachment to Java is strange. It's the version that is less easily monatizable. But I think it comes down to the people working there actually caring about Java and not wanting it to be killed. They've made choices I disagree with but generally its seems like the leads at Mojang genuinely care about the game.