Dacpac deployment via sqlpackage, “DropObjectsNotInSource=True” is trying to drop .mdf & .ldf
If your mdf and ldf files are in a non-default location (or have a non-default prefix / name), you need to add that information to the SSDT project.  This will help the schema compare operation (that occurs when you do a publish) to see that the files are in the right place and don't need to be dropped / recreated.

Right-click your project -> Add New Item -> File Group File

You'll get something like this:

/*
Do not change the database path or name variables.
Any sqlcmd variables will be properly substituted during 
build and deployment.
*/
ALTER DATABASE [$(DatabaseName)]
    ADD FILE
    (
        NAME = [SqlFile1],
        FILENAME = '$(DefaultDataPath)$(DefaultFilePrefix)_SqlFile1.ndf'
    )


Modify that script so that it points to the desired location of your primary data file (mdf) and your deploy should go much more smoothly.

Note that $(DefaultDataPath) is set by the settings of the target instance:



And $(DefaultFilePrefix) is set by the "TargetDatabaseName" in your publish.xml file.