node_modules will constantly expand itself in the Explorer, especially if your defining definitions.
I typically never want this, I think an exception should be made for showing what file is open if its in node_modules to keep the folder collapsed unless I explicitly expand it.
The reason it's a problem is because there are so many files in node_modules you have to collapse it to keep developing, as it's completely useless in most cases to have it expanded and it pushes your work files off screen.
It is now implemented in PR 136905 with the new explorer.autorevealExclude
Inherits from files.exclude
Defaults to same values as search.exclude: **/node_modules, **/bower_components, **/*.code-search
Calls to refresh, selectResource and calls from ExplorerView are all routed to ExplorerService.select(), where the reveal check occurs
Recursively checks from the file up to the first root child, if any of them match a pattern then the file is not revealed.