I’m pretty sure many people just don’t care about SCP licensing when releasing a commercial title related to it. But it’s quite explicit about derivative work: https://scp-wiki.wikidot.com/licensing-guide
I just suppose that the SCP community just have no way to actually enforce their license, so commercial titles do happen. A good example is Control, which is strongly SCP related, but not officially related, because of this license (the devs did mention that in an interview)