Not using social media is considered a badge of honor by many. Not using the web (although that's not entirely true in RMS' case, he just heavily limits it [1]) should be considered a commendable feat, too. Since it's RMS, though, it's just another opportunity to disparage him.
He thinks that non-copyleft licensed projects can't work when there are tons of counterexamples.
Where has he said they "can't" work? The FSF lists scenarios where they endorse non-copyleft here: https://www.gnu.org/licenses/license-recommendations.html
RMS himself has encouraged use of non-copyleft in the cases of e.g. Qt and Ogg Vorbis, either as transitional licenses or as means to free up the software when the alternative would have been remaining proprietary. He says as much here: https://lwn.net/2001/0301/a/rms-ov-license.php3