Mods is part of it, but the biggest reason my 12 year-old insisted on switching to Java is because he says redstone behaves differently.

He'd try to recreate a cool build he saw in a book or online, and get super frustrated when it just wouldn't work in Bedrock edition.

However, I feel that also highlights the importance of network effects. There's a huge amount of content in guide books, wikis, online tutorials, YouTube channels, etc., and the majority of it is targeted at Java edition.

Probably because the older version is Java, so if you grew up being intrroduced by people older than you, the Java would have more staying power.