You are comparing apples and oranges here really.
Sas has to fit database usage requirements like:
-maintain dataset header information,
-maintain variable metadata (formats, etc),
-allow instantaneous direct access to any record,
-use fixed length storage (unless you request compression)
-allow hooks for aging, integrity constraints, index usage
-etc.
Excel doesn't do any of that, it just stores in whatever (probably somewhat compressed) format it sees fit that opens the file in a quick fashion. None of the constraints above apply (but others do, like loading the whole file in one go), as the usage is totally different.
As I said, apples and oranges.
🙂