I disagree with the conclusion. I own the domain name sweet.id and it has catch-all email. Apparently some people (all women so far) found my domain name cute,

I disagree with the conclusion. I own the domain name sweet.id and it has catch-all email. Apparently some people (all women so far) found my domain name cute, they use it to register services (usually Twitter). Maybe they think "Email" field in the signup form akin to "Username", something you create instead of something you already have.