I think it's much more related to market segmentation and upselling. If they started shipping 16GB in the base model they'd probably have to price it closer to the current price of the 8GB one than to the 16GB to stay competitive.

8GB is probably enough for most users in most cases currently (not necessarily in a couple of years, which means they'd update earlier) but the cost for adding 8GB would be pretty low for Apple.

I have a Mac Mini from around 2010 that I saved from the recyclers recently. Dusted it off, put in 8GB of RAM and an SSD, and it booted up Windows 11 just fine. However, as far as I can tell there is no up to date MacOS available for it because Apple considers such a thing too obsolete to support.