Exactly. The app store's gross revenue was $54 billion last year. [1] Apple has a very strong incentive to make sure the only good way to deliver apps on iOS is the app store.
Interesting numbers. I see, "gross revenue" means:
> In the last reported year, customers spent an estimated 54.2 billion U.S. dollars on on in-app purchases, subscriptions, and premium apps in the Apple App store.
So, roughly 30% cut goes to Apple - which is around 16 billion; and developers got the rest, around 38 billion.
With PWAs, 100% goes to developers. As you pointed out, that's a threat and motivation for Apple to continue racheting up their closed ecosystem, and keep PWAs crippled on Apple devices.
[1] https://www.statista.com/statistics/296226/annual-apple-app-...