They contributed quite a bit of useful things to the ecosystem, and were one of the "F# companies that made-it".
Some of their projects live here: https://github.com/jet?language=f%23
An old HN thread on why they chose F# exists here: https://news.ycombinator.com/item?id=9971412 (though the link is broken, comments still exist).
As an F# enjoyer, it's not surprising that this happened. I've seen quite a few companies migrate to Java from various languages. Casting aside syntactical or language-feature niceties, there's just no substitution for the production-maturity of the Java ecosystem.
Plenty of open-source tested-at-scale libraries being put through their paces at large organizations taking in tons of traffic. Best-practices out-of-the-box adapter libraries for most infrastructure. First-party (actual first-party highest tier of coverage) libraries for communicating with the most common infrastructure (All of AWS, elasticsearch, kafka, cassandra, etc). Even with all of the open-source mindshare, most can have an extreme amount of information availability and support with the common core pieces like JUnit, Spring, Hibernate, and the accompanying set of libraries that usually join those. JFR is to my understanding still the only one of its kind.
I'm grateful for what everyone in the F# and dotnet community has done and continues to do, but even in dotnet (which is probably the closest competitor for production cloud web-services), you're spending a lot more time on writing and wiring up supporting libraries for things that the Java stack does for you out of the box. I prefer many small things in the dotnet world to the jvm world, but at the same time I can't deny that I'm much more able to focus on core business logic and concerns when working on a spring project than when I am on a .net 8 web project.