Writing a language, even a DSL is a lot of work. It's not enough to just make a good language, there's also a whole world of tooling support that people expect nowadays.
Also ultimately it was hard to sell the idea of living in a different file format from the rest of your code. This is always a tough sell for DSLs. Even languages as good as CSS and SQL struggle with this for a lot of devs.
A JavaScript-only implementation of robot suffers a similar fate as a DSL without proper tooling, as states and actions are just some custom strings that need to be repeated, no? An implmenetation with good types would provide useful autocompletion, and I can see there was a similar conclusion and types have been implemented with generics. Haven't used it yet to confirm the behavior (at a first glance it seems like a few more strings would need to be inferred), but it would be helpful to mention this somewhere for us TypeScript folks.
Also ultimately it was hard to sell the idea of living in a different file format from the rest of your code. This is always a tough sell for DSLs. Even languages as good as CSS and SQL struggle with this for a lot of devs.