As someone who's worked on a lot of collaborative technology, I find it weird how most of the interest in collaborative editing is confined to the web. As I understand it, Figma's internal collaborative engine is written in C++ anyway.
Collaboration is also much more useful when you're not limited to only working with people using the same OS. Multi-platform distribution is built into web apps, but it takes a lot more effort to create good native apps on several platforms.
Also, of course, no need to install anything on the web, which is important for frictionless collaboration.
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It's no surprise that both desktop and mobile OS-s are very much not optimized for cross platform development. It's a feature (for owners of those OS-s), not a bug.
A primary thing Figma understood better than pretty much anyone else is how collaboration among different teams (not just design) works in product development.