To be fair, you have to pay the Apple tax to use Apple Numbers. It's not monthly (or even a subscription), but it's not a one-time payment if you want the ability to use it over a long period of time.
Once in >5 years is nothing like a SaaS, especially since it's such a tiny part of a product. Even with the traditional software there'd be no guarantee it would keep working for longer than that, e.g. on new OS versions, especially with more specialized software which is a lot of the market for such things.
