This is a consequence of AST trimming that gopls does to reduce memory. There are other similar issues (for example #50196).
IIRC AST trimming provides modest but not major benefit to most users (~25% memory reduction). I am not sure that is worth the loss in precision. I would like to remove our AST trimming in favor of teaching gopls to load fewer packages, but have hesitated to simply remove it before we have offsetting optimizations. Maybe we should.