It feels bad to make a database choice which isn't capable of supporting lots of writes. Lots of things start small but get big unexpectedly, and if you choose sqlite then now you have to rearchitect things.
Lots of things predictably don't. It seems like bad engineering to operate as though everything will. Especially in appliances/"IoT" and other embedded use cases, that line of thinking can drive production costs up a lot.
In the context of embedded things of course you should use something like SQLite as opposed to postgres, because there aren't going to suddenly be millions of people using your CO2 monitor (for example). But for web stuff you can plausibly have user counts that span 6 or 7 orders of magnitude, so you want to be prepared for that.