Why do I still receive texts from non-contacts despite the setting to block them on iPhone?

I turned on the setting that prohibits text messages from being received by anyone not on my contact list, however, I still get plenty of those messages. The iPhone even puts a little subtext in there that says this person is not on your contact list. My first thought is “no kidding.“ My second thought is “then why do I keep getting these messages?“ or is that button in the settings like the proverbial light switch in an old house that doesn’t seem to operate anything?

[Edited by Moderator]