Comment by bitwize

Probably due to the slow processing speed. That thing had like a rinky-dink Z80 and the most basic of graphics chips[0]. It probably couldn't do much besides a simple frame buffer, so you saw the CPU draw the entire screen, laying down the outline vectors and then flood-filling enclosed areas with color. There is something comfortingly "80s graphics" about watching this unfold in front of your eyes, similar to watching an old CAD drawing regen, or the effect in videos like Advanced Video Group's "Bearobics": https://www.youtube.com/watch?v=wWMNsuIeY0Y

That said, I find it grating when I watch programs like Microsoft Teams draw themselves visibly, like old Windows 1.0 programs.

[0] The graphics logic is entirely custom, implemented in a Toshiba gate array, and it isn't something well-known like a TMS9918A or something else based on that design.