I'm still following some of the same Java Edition YouTubers that I've been following for more than 10 years now (and they're still producing content weekly!). I still occasionally break out an old version of Java Edition and play some of the old mods that I liked back in the day. Many of those aren't maintained any more because the creators have moved on, but many have stuck around (Biomes O' Plenty and Iron Chests have a 1.21 release, and Applied Energistics has one for 1.20 that was last updated today). Plus we still get amazing new mods like Create.
I don't think it's that the old Minecraft has really gone anywhere, it's that, like the internet as a whole, it got so popular that geeks and nerds stopped being the majority. The existence of Minecraft Bedrock brought Minecraft to a bunch of kids who would have never grokked the wild west of Minecraft Java. But its existence hasn't taken away from everything that Minecraft Java still is.