Of course someone could say their mother's maiden name was "zx81 Tamoxifen lion soap" but how many would give answers that aren't actually their mother's maiden name? And some places/services don't even allow such answers.
Of course, giving obscure answers can be problematic as well. Do you need to change security settings? Forgot your obscure answer? Didn't store it as securely as the password cause you didn't think you'd need it? Congratulations, you're locked out of changing your settings.
For a real world example, adding 2-way authentication to EA's Origin accounts requires answering the security question. Can't remember it? You can't add additional security to your account. There's complaints on their forums about this. Only way to reset the security question is through customer service, which is apparently difficult to reach.