Red Hat didn't "close up the source" to anything. All the source to RHEL is available in CenOS Stream's git repos. All of the source to all Red Hat products is available in upstream projects too. Nothing's "closed".
What was announced was that the source to RHEL would only be publicly published in git (with history, tagged releases, etc.) instead of publically available SRPMs (unless you use a Red Hat account — even a free one — then you could also download SRPMs).