@thelinuxEXP I've been thinking about this and there's only one logical reason I've been able to come up with.
If sideloading becomes an option, then apps that would have been in the app store might instead only be available via side loading. These apps, some of which might be "essential" apps, would not be subject to scrutiny that they would be otherwise and are thus able to get away with more stuff. As an arbitrary, hypothetical example, Twitter (which is "essential" for many) could become sideload-only and begin tracking much more than Apple would allow them; or an app that becomes sideload-only could later be the subject of an attack an be replaced with malware (if it were in the app store it would presumably be blocked from reaching end users).

@mithicspirit I don’t think any serious company that wants their app to be actually used and downloaded would deprive themselves of the preinstalled store users have gotten used to for 15 years, but we’ll have to see!