That's a good point. They are taxing paid apps and not taxing ad-supported apps. Which incentivizes the ad-model and therefore reduces the number of paid apps.
This has been the case since the beginning with mobile app stores so who knows how the distribution of paid vs ad-supported apps would be if this wasn't the case.
On the flip side, Apple is incentivized to encourage paid apps and subscription based apps in order to collect revenue. Purely advertising-driven apps just cost them hosting and support.
Historically they have not offered enough options here, such forbidding time-limited trials and not providing specific guidance for companies who wish to sell paid upgrades to new major versions. Apple's (arguably workable) solution here was entirely based on subscriptions.
That said, the ease of use of subscriptions and the high variability of billing amounts/periods has caused them to be the preferred mechanism for App Store scams.
This has been the case since the beginning with mobile app stores so who knows how the distribution of paid vs ad-supported apps would be if this wasn't the case.