The problem here is not with the wordpress source, which anyone could fork at any time. Likewise any open source licensed plugins.

The problem here is the pernicious, and ever more common, enshittification of open source ecosystems and the open source ethic - wordpress being a particularly acute case. I say this as someone who has been online since before a broad public internet even existed, never mind the WWW, and has been using and advocating for open source wherever and whenever possible.

Most of the large, broadly beneficial and well matured open source applications or platforms that still hold the original ethic have been through at least a few significant traumas and shakeups and yes, forks. How wordpress (by whatever name(s) any fork(s) might have) fares remains to be seen. Then there are those who, in recent decades, have applied a thin veneer of "open source" as a honey trap to capture and lock in users. The laughable "community versions" that are blatant crippleware, for example. The deployments designed to be absurdly difficult to self-host, to drive business to a SaaS provider. And most obviously, the holding of service/trade marks and similar non-code IP by individuals or privately held corporate entities, rather than foundations set up to safeguard the IP, the source, and the ethic it is based on.