It's not an indicator of intelligence, but mail providers (including Google) could offer this if they want to, with a simple "Choose a personalized email address, like [email protected], for $9.99 per year" radio button on signup. They don't do this because:

1. Most people will choose the free option, so it wouldn't be much of a useful revenue stream.

2. People having @gmail.com email addresses is a little bit of zero-cost marketing for them.