I disagree, the apps facilitate their business but Uber and Airbnb aren't in the software development business, as they don't develop software for sale as their primary means of income.

To paraphrase, they're both software companies who happen to do rentals and cars. There's also nothing in that law which talks about core business. It's to do with work in the normal line of business, in other words - work which is regularly performed by the company, rather than specialist work for which a contractor is required.

No, they're both taxi services that happen to use software.

Core business is understood to mean primary revenue generating activity, which is getting paid for facilitating rides. They don't charge any money for the use of the software.

technically Uber is a software company according to its incorporation and Rasier is the transportation services company.