inserting records in a sqlite database does not change its size but

I have a SQLite database with about 100 records inserted in it. the size of the file on my disk is about 65 KB. It was the same before and after the insertion of data. I compressed the file to .tar.7z format. As I keep adding data the size of the database file stays the same but when I compress it I see the size of archive file growing. Why is that so? Could someone please explain the reason for this behavior I am observing.