Our editor integration is completely editor agnostic. Deno implements the Language Server Protocol [1], which essentially all editors support. Because of this the new inlay hints feature, is supported on all editors that support inlay hints and use our LSP integration. The Jetbrains integration for Deno uses our LSP, but I don't know if they support inlay hints yet.
VSCode is the only integration that the Deno core team maintains and develops. A rough poll indicates that about 80% of Deno users use vscode.
JetBrains/WebStorm now utilises the Deno language server directly (the same one that the VSCode integration uses) but they control how features are expressed in their client and when they deliver them, something the core team can't directly control.
So for various reasons, VSCode ends up being the focus.