Comment by ternaryoperator

I can't comment about github.io, but to address your larger concern, this is in part due to the vast amount of cybersquatting. It's now very difficult to get meaningful domain names in the top TLDs, so companies and projects are being pushed to other TLDs. It's easier for techs to move to non-mainstream TLDs than for consumer-oriented companies, b/c we're comfortable with using them, whereas the average consumer will be confused or hesitant to click.

The trend will eventually be that, except for established historical domains (.co.uk, and a few dozen more), most TLDs won't signinfy anything. That's already happened with .ly, and is happening now with .io and .co.