IKEA wants to render a lot of its product illustrations instead of having huge photo studios, that's probably why they are active in computer graphics.
They probably have custom renderers for rendering the flat/cartoon illustrations for the assembly instructions, and PBR renders for rendering realistic views.
Grab a bunch of of these resources and put them in a box and you have living room design without having to manufacture, assemble, light, and shoot it in the real world.
eta: ope, I see someone beat me to the same comment.
* "Multiverse of madness - how we render millions of doors": https://www.youtube.com/watch?v=HXEVncxtmxg
Product visualisation seems to be a bit of a recurring theme for Blender talks over at least the past couple of years.
He could have solved most of his issues by switching to a 3d configurator. I have built a custom threejs engine over the last decade that allows you to declaratively define materials, texture, repeating geometry, ... In a few lines of code. It has primitives like flexible grids, cloning, CSG operations etc.
I currently use it mostly for outdoor living structures, but implementing doors and/or floors for this would be trivial.
If you'd do this using my engine, the biggest thing left would be gathering the requirements and conventions... So I'd build a configurator for door configurators that allows suppliers to easily create their own configurators...
In fact, I'm doing this right now for terrace roofs/sun rooms.
Turtles all the way down...
It's much easier to digitally assemble those models into a virtual kitchen scene than to build an actual kitchen. Especially things like a sink where you'd need to cut a custom countertop to mount it.
The simple answer that you can infer from the video is that they make very high quality models for the design stage, which is definitely cheaper than making prototypes in all plausible material combinations.
Then you can use those models for the simple product pictures too, and packing a 3d model with generic clothes is probably faster than having a prop department do it.