Yeah, it is incovenient when you play Java and other people you know play Bedrock (or vice-versa). There is a community-made plugin called Geyser that allows Bedrock players to play on Java servers (it can be buggy sometimes but it is the closest we have to Java-Bedrock crossplay).

Java is the original and Bedrock is the C++ adaptation that came about once Microsoft bought Minecraft. Microsoft couldn't really justify getting rid of Java edition because that's what the entire PC userbase was using at the time, and they've gotten very used to the features it allows for. Namely mods. However they still wanted to unify the casual playerbase and better monetize the game.

On the topic of monetization, Minecraft originally had this nasty little clause (for Microsoft) written in I forget either the ToS, EULA, or what, but it essentially guaranteed all future updates to the game for free. I believe it also made some other guarantees about no MTX, should never have to pay for servers, etc but those I'm less certain about. Around the time MS bought the game there was a lot of talk about how the only way they'd really be able to get out of that guarantee to the millions of players who already owned "Java edition" (just regular Minecraft back then) was to make a Minecraft 2.0 that didn't have that clause. Their approach for that problem appears to have been bedrock edition which they maintain alongside Java edition. Because it's not the version they bought, they can make changes to the legal agreements including charging for things Java Edition users have a guaranteed right to.

Those are the two main reasons I'm aware of for the two editions. I believe the majority of the PC playerbase is currently on Bedrock Edition so although they would have some backlash if they suddenly decided to axe it I think the majority of the playerbase would chug on like normal. Afaik the main reason they don't is because anyone who purchased Minecraft before there was a "Java Edition" would have a legal claim to say Bedrock is clearly the same game under another title, they're not getting future updates as guaranteed, and are entitled to either updates or compensation. And I can't imagine MS is interested in litigiously pissing off millions of players.