Honestly, I'm just spitballing here, but it's not like the Raspberry foundation is making its own silicon. They're using what exists. It's probably a simple case of the chipset they chose supporting it, so might as well include it.
They are making their own silicon (see the RP1 at [1]) and obviously have very significant input as to what Broadcom puts into the main SoC, a chip that is primarily now made for RPi needs.
Rp1 doesn’t deal with video, and having two displays is very reasonable for all kinds of things, including display kiosks, points of sale, etc
Even for a robot. They don’t need to be 4k, it I guess that’s just normal these days
I could be wrong, but iirc the HDMI they use and full size HDMI are pin compatible. It's likely they just chose the smaller connector so they can break both out and have a smaller board footprint(as opposed to having a larger board or only providing a connector for one HDMI port)
