Which you then have to type out every time. Laziness wins: they will be shorter.

The assumption is that the product is for non-savvy users. They might not even understand what you wrote up there.

Autocorrect can help here, but dictionary words are easily brute-forced guessed. And - more importantly - that hypothetical user would have to come up with that idea in the first place. But people who come up with such ideas usually already use password managers anyhow.