Is that a new feature? Pretty sure it didn't a few years ago. If the thing I need needed the libfoo C library then I first had to install libfoo on my computer using apt/brew/etc. If a new version of the PHP extension comes out that uses libfoo 2.0, then it was up to me to update libfoo first. There was no way for composer to install and manage libfoo.
Is that a new feature? Pretty sure it didn't a few years ago. If the thing I need needed the libfoo C library then I first had to install libfoo on my computer using apt/brew/etc. If a new version of the PHP extension comes out that uses libfoo 2.0, then it was up to me to update libfoo first. There was no way for composer to install and manage libfoo.