Serious question - do they not have function keys because that's just the models shown? Or is it normal for keyboards like this to not have them and if so why?
This is one of them. Function keys are reached vi a modifier.
There are others: https://www.modelfkeyboards.com/product/classic-style-f122-m...
F24 for life!
One annoying thing about macOS is that it has a very limited collection of key codes. I tried using F24 for window placement but it was ignored, so I had to back off to F16.
So instead they usually have more modifiers and utilize the thumb for way more than the spacebar. The varieties are endless.
Arrow keys are right on your home-row, it is just a thumb-press away, as is F-keys and the numpad (numpad works better if you have an otrholinear layout rather than the staggared keys normal keyboards have).
This is true of keyboards like the Moonlander, or the Planck (which is even smaller than OP's keyboard).
But, OP's keyboard has a big spacebar.
I reckon there are two families of "small keyboards": those with a big-spacebar, and those with multiple thumbkeys.
With the big spacebar, I feel vindicated to see the replies linked to say "I don't need F-keys because I don't use them frequently".
Whereas with the Planck, the Planck is as small as it is (as stated on the video on olkb.com) in order to minimize hand movement/stretching from home row.