If they allowed side-loading, they might not capture 30% of revenue from apps sold through the app store. If they disallowed scams, they might not capture 30% of the scammers' revenue.
I honestly believe that some sort of side-loading option would be best for any cynical Apple interests long-term and for developers and for users.
The current course of action just leads to developer frustration (which is fine until a disruptive player enters the market), a super shitty store that leaves customers pissed (with scams, etc.), constant churn in rules to try to appease everyone and kick the can another 2 years (like the 15% reduction), and worst of all, unwanted attention from regulators that could have chaotic effects.
This would also disincentivize jailbreakers, as fewer power users would be interested in pursuing the 100% amount of freedom that jailbreaking allows.
You could even go all of the way and have Apple adopt a "can't beat us? Join us" mentality towards independent app repositories outside of App Store by providing their own APIs and SDKs to run your own third-party app store. Again, architect it to automatically include security checks. Tie in subtle ways for Apple still to get a cut and a measure of their control.
This is far from a concrete description of what "third party stores brought to you by Apple" would look like, but if there's any company that could square the circle and make it a reality, it'd be Apple.
That is what I have been saying for quite some time. If Apple separate their Game Store and held some of those API, they have effectively kept 80% of their App Store revenue intact even if they allowed side loading.
Then at the expense of 20% of their App Store revenue, they can think what is the best possible balance to the problem here.