[kjksf]

Maybe because Deno folks are pragmatics and not fanatics.

Rust is faster than V8. I'm not sure if ALL Deno tooling is written in Rust, but it makes sense to write, say, Typescript => JavaScript converter in Rust if it's 10-100x faster.

All that tells you is that if you want a very fast Typescript => JavaScript converter then you too should use Rust (or Go or C++) and not JavaScript executed by V8.

But writing a web app?

You're free to use Rust for that as well but millions of people chose nodejs instead and those are the people that might choose Deno in the future.

[SOLAR_FIELDS]

And indeed, you can see as a great example from the discussion on this thread how they eventually arrived at relying on Rust for most steps in the tsc toolchain: https://github.com/denoland/deno/issues/5432

The conclusion reached there is as you have stated: Rust is simply an order of magnitude faster in most cases.