Why can't F# open static classes?

There is a suggestion for it on GitHub. The original suggestion, has a comment from Don Syme:

Yes, this should I suppose be implemented to match the corresponding C# feature, since static classes will begin to be more common coming from the C# world.

I would recommend voting for the issue on GitHub (react with a thumbs up). If you have any comment to add then people may become interested in this again.