"Claude Code uses Bun" is the reason that's given. But even though Anthropic tells us that "coding is solved", instead of rewriting Claude Code in something other than JS, they bought a company that made a JS runtime and then did a mass rewrite of that JS runtime.
Bun was a startup. Startups can go out of business, and then you are now scrambling to move your code to something else. They could also be bought by someone who has different priorities regarding future development than you, and that's also a risk.
The simplest solution to these problems, if you have the capital, is to buy them.
"Claude Code uses Bun" is the reason that's given. But even though Anthropic tells us that "coding is solved", instead of rewriting Claude Code in something other than JS, they bought a company that made a JS runtime and then did a mass rewrite of that JS runtime.