Maybe you don't use it very often? For months before the recent chaos it was very reliable. The fact that it's working today is only because I fixed it, Twitter didn't change anything.
It's disabled on nitter.net to reduce load while this new solution is being tested.
Check the instance list for updated instances, most of them have RSS enabled: https://github.com/zedeus/nitter/wiki/Instances
This isn't actually true, the "Instance has been rate limited" error was a false flag. It turned out to be a bug in the API token parser, found and fixed by a contributor. Nitter instances have yet to run into a real rate limit.