Rextester is going to become a paid service. There is going to be a price for individuals something like 3$ a month and something less for groups.
The first step in implementing that is mandatory login for all users that want to execute the code.
The simple sign-up method is deprecated as there are simpler methods - currently via Google and Facebook. Later Github will be added too.
We use these login methods as they are the simplest and safest options for us and users. We collect minimal amount of data - just enough to uniquely identify the user and we store hashed version of that unique identifier in db, so we don't even have your email.
Alright, this idea probably not worth the effort, so I've removed the login restrictions.