This is my understanding:

1. Ruby Central hosts, maintains, and sponsors Rubygems and Bundler

2. Based on recent events, it was possible that credentials were stolen (https://www.bleepingcomputer.com/news/security/60-malicious-...)

3. They decided to lock everyone out until security issues could be resolved

It makes sense to me from a security standpoint, but their communication has been terrible which has led to a lot of speculation.