No metal waste during production with louvers - it's just bending metal. Lots of punched hole pieces to manage with holes. Also, if louvers are formed correctly, the total flow area of the center tube will be a bit more than with holes, so that helps reduce the delta-p vs flow a little bit. If louvers are not formed correctly, then the delta-p could actually be increased, and if louvers are almost closed, that could make the delta-p so high that the filter's bypass valve may open way more than it should.
Makes sense. Thanks for the explanation!