I don't know a single person who used Eclipse after 2020. Don't you think that supporting Eclipse might be a viable marketing strategy to get people who are stuck in the past on board with newer tech, as if anything, they will probably move on to IDEA?
> Ex. MS offers an official LS rather than saying "we don't support other IDEs because Visual Studio licenses."
MS is a bad example because they recently literally took away a feature from dotnet to push it into VS and drive sales, which was met a HUGE backlash from the community. Dotnet IS the driving force behind Visual Studio. JetBrains actually came in and took a piece of that from them(thankfully, because I personally hate vs/vscode). Like other answer to your comment said, JetBrains doesn't owe anything to anyone. If there is already a Language Server for Kotlin, great, I don't see how a product-based company could benefit from making something that drives people away from their (already free) product...