PHP 7+ hasn't added that much in terms of new APIs — (e.g. libsodium in 7.2, and it's typical function(target, arguments) stuff). It added strict typing and a very significant bunch of ergonomic/performance changes.

I'd say half the reason to call it a quick evolution is how fast it's being adopted compared with the glacial progress from 5.2 to 5.6, or Python 2 to 3.

Also a third half of the freshness has been adoption of packaging and coding standards.