The value to the company was provided in Illinois, with bits inside of Illinois. The company doesn't value bits inside California that it cannot access. They compensated for bits they can actually access within Illinois.
>Why would the intellectual property the employee generated be worth nothing simply by originating in California?
It may be worth something to someone in California before it's exported, but that transaction never happened. In this case though the actual transaction took place in exchange for a product inside Illinois.
>In other words, if a bottle manufacturer in Illinois sourced raw glass pellets from a plant they owned in California, they would be deriving value from a source in California. The glass is not worthless because it hasn’t been converted into bottles yet.
This is actually a great example. I buy ammunition online from a company in Oklahoma, where all the business and employees of the ammunition company resides. Yet I pay sales tax here in <my state> based on recent court rulings regarding 'internet sales tax' which state the tax is where the transaction took place (/the finished product goes to), not where the company and/or workers physically resides. It wouldn't make sense at all for me to pay sales tax to Oklahoma, even though the ammunition and even all the physical presence was initially generated there. I pay sales tax where the transaction and actual value to me, the buyer of the goods, actually are. Using the same analogy from this court ruling, you would pay tax on the IP you bought in Illinois and not where it was initially produced California.
>The employee is providing intellectual property across state lines, which is why the state can enforce laws on that value that originated from within their jurisdiction.
The employer is buying IP within their state lines of Illinois. You may be arguing the 'employee' is actually misclassified and is an illegal exporter who is a business owner in California with an export and bit smuggling business. Go after this 'employee' (bit smuggler), not the person buying bits in Illinois.