I've wondered about this question too and not understood the concern about wavy pleats. Assuming the media wasn't wavy from the factory, it implies stresses are being applied. So the questions should be where is the stress coming from and is the filter not designed for the associated stresses?
My guess is the media expands as it fills with oil. The long pleats will expand more lengthwise, and with a rigid top and bottom, they're likely to start bending/bowing and creating the waves we see. The media itself is pliable, so I don't think the stress of the moving material loads the top and bottom where it's glued firmly to the metal caps. But maybe it does and this creates a stress point that can start to tear over time.
All speculation without any real science. Would be cool to know if the bends happen soon after installation or over the course of the cycle...