The reason for the saving was enforcement of constrains in various Access tables so a subtle entry error in Excel was discovered.
The transition to DB file was done by a single person in a month who had not worked previously with DB (however he was young and talented programmer I must admit).
And the Access DB in a single file with its UI was quite similar to Excel so guys maintaining it quickly learned it and really liked it.
So it is still puzzles me why such single file DB with nice UI are not more popular? Why it is always Excel?