It's not an illusion, 1q2w3e4r5t is indeed better than aaaaaaaaa, even if it's just the numbers interleaved with qwerty (and probably easy to brute force generate up to it).
>if I use "aaaaaaaaa" as a password on a website I know full well what I'm doing. So why even bother?
Because not everyone who uses "aaaaaaaaa" (or "1q2w3e4r5t" for that matter) knows "full well" that it's insecure?