I figure it is on account of the desirable situation you describe in your other post not obtaining: in order to satisfy the goals of the IDE, it attempts to go beyond where the compiler parser would stop, as the compiler is more of a batch than a responsive one, and sometimes the IDE gets it wrong. As you say, batch to responsive is the difficult way to go.
In addition, I suppose that there are people hard at work applying ML in tools to help understand incomplete code and mitigate the false positive problem of traditional static analysis. I can imagine probabilistic parsing being useful in this case, but not so much in compiling.
Bad language plugins in an IDE can show you this. Sometimes I'll be using a niche language with someone's side-project plugin that has some issues even though it's correct, like when its file-formatter can't parse the code and fails with an error even though it's valid code for the compiler.
