It's not a graphics mode. It is just a resolution from the graphics mode, repurposed for the text mode. The reason possibly being the 640x480 resolution is universally supported while 720x400 is not - for example my HDMI TV can still display 640x480.

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bananaboy 3 days ago | parent [-]

CRTs were still commonplace though based on the bios dates in the blog. So 720x400 would still have been well supported. It’s strange that they did this!

	▲	the-rc 3 days ago \| parent [-]
		Unlike CRT screens, LCD ones from that time had usually a fixed resolution and wouldn't resize the image on the fly.