To secure network effects for themselves. This is one of the reasons the ASF was founded.

https://httpd.apache.org/ABOUT_APACHE.html

> We realize that it is often seen as an economic advantage for one company to "own" a market - in the software industry, that means to control tightly a particular conduit such that all others must pay for its use. This is typically done by "owning" the protocols through which companies conduct business, at the expense of all those other companies. To the extent that the protocols of the World Wide Web remain "unowned" by a single company, the Web will remain a level playing field for companies large and small. Thus, "ownership" of the protocols must be prevented.

They wouldn't. But the GPP seemed to be implying that we should be grateful to commercial entities for the existence of those useful open projects, when in fact if the commercial entities had their preferred way the projects would not be (as) open.