The title doesn't make it clear that it's actually about TypeScript plus Deno-specific syntax — and Deno's LSP doesn't run in a worker [1].
They could have also contributed to the effort. You can also add types to monaco typescript. I don’t see a need for a Deno specific LSP, am I missing something?
The second biggest deal is that the Deno LSP also includes a full linter, versus for the full experience the Typescript not-quite-LSP is often paired with the ESLint VS Code extension and a large eslint install.
Deno's LSP is also sometimes preferred for being a single Rust binary that runs quicker than Typescript's not-quite-LSP (plus or minus ESLint's non-LSP). It may be interesting to see how Golang Typescript's real-LSP fares in comparison in a future version.