I wasn't involved in that decision at all, but FWIW, TypeScript has a strong type system and is concise and expressive at the same time. Combined with the largest ecosystem of libraries and tools of Node.js, I think it's a solid choice.

Can you ask the people who were involved in that decision? It’s important to my team that when prioritizing new features Pulumi is talking to and making an effort to understand the needs of infra & backend developers.

Alternatives like Python and Go have weak type systems. Luke, who answered you above, is one of the original designers of TypeScript. And many Pulumi folks have background at Microsoft. Btw, AWS CDK is mainly TypeScript too.