CAPTCHA: Completely Automated Public Turing test to tell Computers and Humans Apart.
These things have one job. Any time they fail to identify a human, they have failed at their job. How they go about administering the test, and (to a large extent) what the human does in response, should be irrelevant. I know that's hard, no-one said the job was easy, and the companies developing them are the ones making claims about their efficacy.
If you want to block 100% of bots, don't put your stuff on the Internet. If you want to block bots and allow humans then you're going to have false negatives. Failing to acknowledge them is dishonest.
None of which stops me filling them out when I encounter them, but I don't have to like it.