[JdeBP]

There's an underlying assumption about "target audience for this editor" that you both share, that others, I suspect quite a few others, do not.

For starters, there's your assumption that there is "syntax" to be highlighted. Not every text file is something written in a computer programming language.

[seabrookmx]

You're right, I do assume most (90+%? of) people that are looking for a terminal editor are likely developers.

In fact I'd put money on it, but sadly do not have any evidence to back it up.

If you have evidence to the contrary I'd be intrigued!

[pxc]

You might not be wrong about percentages, but there are famously some Emacs users who for into it for Org mode or academic writing, including even some who learned to program long to better customize their Emacs setup and eventually became contributors.

But these are amateur geeks or geeks in the making who probably don't mind having the capability of syntax highlighting built in, even if for some purposes they want it turned off.