Presumably - Sketch is great software, well built, but the fact that in late 2020 they still have to write "And soon, the ability to collaborate in real-time" is the the best counter-argument to building native for me personally.
As a designer, I’d much rather collaborate via the Git-like system of Abstract, committing changes and merging pull requests than have things happening elsewhere in the file I’m working on with no versioning or notification.
Real-time collaboration has never been in demand among developers, has it?
VSCode's liveshare feature is getting very close though and it does feel great to attack a challenge together from time to time.
The reason MS Office struggles with this is that rebuilding an app that wasn't originally supposed to work in such mode is way harder than building from scratch, and they probably don't really need it that much to push themselves in such an adventure.