There's a simple reason the decision does not provide the explanation you are looking for: that's not the role of the court. The California legislature, by statute, and the Industrial Welfare Commission, established that there needs to be a distinction between employee and independent contractor. The courts have the role of setting forth a rule consistent with California statutes and IWC wage orders that courts (and, by extension, the public) can use to determine whether someone falls into the "employee" or "contractor" category. It does not matter to the court WHY that distinction exists, except to the extent that why informs what test to use to determine who is and who is not an employee under state law.

Courts commonly rule on intent, and laws generally have an intent discernable from the language of the legislation or the records of is legislative debate. This gives courts a way to disambiguate unclear cases like this one, and it's typically vital to have some intent to fall back on, since laws don't make sense otherwise.

These confused rulings are exactly what you expect in the absence of such a mooring. They can't give a reason why my rules A or B are absurd, except for whether they match some hard-to-parse guidelines.

Example: If the employer requires you to bring your own tools, that somehow makes you more of a contractor, even though that's a greater burden on the worker, but someone decided that such instances "feel" more like contractors. Exactly what confused governance and legislation look like.