The problem with putting USB-C video on there is that USB-C is DisplayPort, and there's a good chance for various reasons (last time it was said that at least historically, the Raspberry Pi is a cut down version of a Broadcom chip that was used in a set top box or media player or something) the SoC only has an HDMI interface block on it and not a DisplayPort one. Thus, supporting this would require the addition of at least a converter chip, plus a Type-C port chip, which probably takes up valuable BOM budget. Given how few ICs are present on this board, this was probably not a feature very high on the priorities list.