> meant to be an easy to use all-in-one friendly to beginners
Unlike the "normal" Raspberry Pi this device has a fairly focused use case that you have summarised well here. It is designed to be plugged into an HDMI TV and used as a PC, with the great bonus of a cool GPIO connector. You make some choices and you make some sacrifices to meet cost and space targets. This also isn't an iPhone that costs $800.
As for fitting the HDMI on, there isn't loads of space for a full size port. I'm not saying it would be completely impossible but it would be challenging. Have a look at the photo of the board in this post:
https://www.raspberrypi.org/blog/designing-raspberry-pi-400/
The non obvious thing looking at that photo is that the keyboard slopes back so you only have height at the front. Non-micro HDMI are surprisingly deep, without CAD looking up parts and looking up parts I can't tell if just wouldn't fit at all, but you certainly wouldn't be able to get much behind it. Note also that they couldn't work out a way to sensibly route the USB to the other side - it's clearly a busy board.
