Because they have a product that makes $1bn+ a year that depends on having a good, stable, cross-platform JS runtime.

I'm wondering if Bun would be a good embedded runtime for Claude to think in. If it does sandboxing, or if they can add sandboxing, then they can standardize on a language and runtime for Claude Code and Claude Desktop and bake it into training like they do with other agentic things like tool calls. It'd be too risky to do unless they owned the runtime.

Why would Sun then Oracle own Java? Why would Microsoft own .net? Why would Apple own swift?

IOW look where the puck is going.