When we add lots of documents in a database, that view index size (not full text index) grows quickly. However, when we delete the documents from database view index size does not reduces.
We need to update each view or folder manually by pressing Shift + F9. Post this, the view gets indexed and also view index size reduces.
Another way is to run updall -R on the databases.
It would be helpful to reduce the DB view index size automatically avoiding manually updating the view.