On the Mac, lists are this really basic thing they added in 2005 or so, along with a few other features (like tables). Since then, they have barely touched it, along with the rest of the text engine—it’s quite out of date at this point, and only relevant for the fact that at one point in time, it was ahead of its time.
On the whole though, it probably has to do with there not being many programs that aren’t word processors needing a really robust and feature-rich formatting interface. You have your email client with the dirt basics; maybe a notepad program that does a little bold and italic stuff here and there, Comic Sans; a bunch of Markdown-based stuff… and then dedicated programs like Word and LibreOffice that put all of their effort into these things. We’re kind of in an awkward middle of all that, particularly in that a lot of people somehow expect us to make both LibreOffice and Scrivener at the same time. Somehow. 
Another problem, with lists specifically, is that there is no real standard way to make lists in RTF, as I understand it. It’s a combination of convention and hard-wiring, and it’s not uncommon for one program’s lists to not work in another’s as a result. Some of our issues stem from trying to coerce two completely different engines, with their own assumptions, into working together.
External folder sync is not a bad idea as well! It’s probably a bit of setup if you only need to shuffle a list around a bit here or there, but if you have a workflow built around using Scrivener more as the content hub and document generator than the text entry/editing UI, then it’s a natural way to go. I totally get that inclination. As a Markdown-based writer, Scrivener’s editor is adequate but not ideal. With some projects I use the folder sync feature with software like Obsidian or Visual Studio Code to act as a kind of front-end writing tool.
In my opinion, there’s nothing wrong with that.