You can find an explanation on the internal considerations re file size after deletes in https://community.tableau.com/message/1011392#1011392
I hope this other post answer your question re. why file size increases.
The same post also presents a temporary workaround (i.e. copying the data into a new table using INSERT INTO SELECT * FROM)
Please let me know if my explanation of the issue was insufficient or if you are hitting any issues with the workaround
During that same forum thread, we realized that we have a bug in our storage management which negatively impacts file size by an even larger factor than we thought.
We are working on fixing those issues and you can expect DELETE to become much better in the future.
Probably, there will be changes in the next two releases (our January and February release; no promises, though) which should make deletion much more efficient re. file size.
Thanks Adrian . Will look forward for the release .