Unfortunately having access to all the pixels that make up a movie or all the words that make up a book doesn’t make either free, and the same thing applies to code depending on licenses

Some open source projects sell recompiled and signed copies and if you want it free, you can compile from source.

It’s a convenience thing…

https://www.gnu.org/philosophy/open-source-misses-the-point.html

License. The owner of the source can still limit what you can (legally) do with it.

In addition to the other comment, a lot of companies typically sell support for their software, not the software itself. That counts for a lot in the business world

For example Unreal Engine is source available. Can't redistribute it, can't fork it and make a new version for the public. Still need to pay Epic when you release a game and make revenue over one million.

Free doesn't mean free. It means free.