Yeah, I’m a maintainer, MacPorts will download a binary if it can. ffmpeg is a weird case thanks to the non-free variants, but even it has some binary installs.

Also, for instance, OpenJDK is a port that is offered and we do not compile that in any way on any system because that way lies madness.

The other reason that macports will build from source is when there isn’t a binary like early on in Big Sur.