The law has already engaged in a lot of line drawing exercises on what the difference between "goods" or "services" are.

A cake is always a good. It's a movable object at the time of sale. So if the cake is already created, there's no personal services component to a purchase of that already-made cake (no matter how much skill and artisan creativity went into it).

A custom designed cake is still a good, not a service, although the work of doing the custom design is a service. And it's a "personal" service if you need a particular person to do it.

Think of it this way: If I go to a bakery and order a custom-designed cake, do I care which employee does which part? Can the bakery still follow through with its contract if it fires everyone and then hires a bunch of new employees? If I don't care who the person is, and am only relying on the bakery (a company, not a natural person) and its reputation, then I'm not asking for a personal service. If I go to a bakery because it's owned by the Ace of Cakes guy, and I commission him personally to design and bake a cake, then it'll be a contract that includes personal services (and will also include a good, the cake). But if I contract with the company, then I shouldn't be disappointed if he just outsources the job to someone else, like an employee in his company.

For a sole proprietorship bakery, where there is only one employee, you'd run into a problem where you're asking a particular person to do a particular thing. At that point, I think it the Thirteenth Amendment would apply if we had a law that mandated that person actually serve someone in a way, with no choice to say "no." But that's a different scenario entirely from the generalized "bake me a cake" situation. The Thirteenth Amendment might look to whether it's a personal service or not, and the First Amendment speech/expression rules might look to whether it's an expressive work or not. An ad agency or a law firm doesn't have Thirteenth Amendment rights (indeed, they're actually owned by people), but they have the free speech rights to refuse to speak on behalf of an unwanted client. So this isn't the only issue out there. It's one of many.

But personal services are special, is all I'm saying.