The settings you've played with only impact the history tables - not the _views that you are going after. There is no way to prevent data in the tables which the views pull from from being truncated.
Consider creating a Tableau Extract of this data as a permanent record, or copy the rows directly to a different database using scripts and/or queries.
Searching the forums for "truncate postgreSQL" will probably land you on a few threads where people have had similar challenges.
Hope this helps!