> Because that's the same domain.

You're again mistakenly thinking of trademark law. Toni Iommi is not a product but a person whose name is not trademarked. He doesn't have a "domain". He just happens to be famous for being a guitar player.

The issue with "Iommi Guitars" is that it gives the impression that Tony Iommi the person endorses those guitars. But Tony Iommi could endorse any product. For example, he endorses a perfume: https://www.nordstrom.com/s/tony-iommi-monkey-special-parfum... If someone not associated with Tony Iommi sold a "Tony Iommi Perfume" that would also be a problem, not because the name "Tony Iommi" is trademarked but rather because it gives the impression that Tony Iommi endorses the product when he does not.

Celebrity endorsements are valuable, and celebrities endorse lots of products that have nothing to do with the primary profession for which they are famous. The actor Paul Newman has a whole line of food products.

Moreover, it's very common nowadays for musicians to use computers heavily, so it wouldn't be surprising for them to get into programming too.