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.
I do not miss Sketch one bit.
At least, with Sketch/macOS the code is executed on the device you can control (to a degree).
[0]: https://www.gnu.org/philosophy/who-does-that-server-really-s...
With locally running app you control when and where the app works, and you have way more options when developer introduces some changes that don't fit you.
Maybe you were trying to say that you can't open new sketch files because your version of macOS doesn't support latest versions of Sketch? That is, indeed, a problem. However, if you work only with internal files, you can simply abstain from upgrading to new version and keep working on the version that works for you. Moreover, Sketch licences do not 'expire', you simply can't receive updates any longer. So you can still work with your files as long as you need, not relying on someone else's actions.
By paying for any tool you are strengthening its position and philosophy, whether you care about it or not.