Its the sheer size, we always had integrated screens which sat within the IP shape, since they have headed past the 200mm mark it becomes pretty much impossible to keep them within the IP shape without compromising the likes of the HVAC (which is what takes most of the behind IP space up).
Screen size is being driven very much by the move to reduce physical switches (something I, and many others, don't like......but designers are weird and all powerful it would seem) so the real estate is being driven by the need to create large touch areas as well as supporting more complex info panels, ADAS (advanced driver assistance systems) is very much not helping here.
It may shrink a bit as the laser projection HUDs (Head Up Display) arrive and project across larger areas of the windscreen.
You really don't want to know how many display outputs I am being asked for for the 2030+ architecture!