I disagree. It IS that simple. Not only has Android had support for mice for years (without any ill effect), jailbroken iPads (starting with the 1st gen iPad) could install an app to use mice. It didn't interfere with the touch UI and, like Android, was optional. I used it back then and it was excellent.
Could be
The fear that adding support for mice would result in apps requiring mice. That is an unfounded fear because (A) Apple has a tight grip on the app store and could impose restrictions on mice exclusivity, and (B) history has shown that optional accessories don't drift into becoming required.
Also true. I assume that apps can be used with and without Pencil and with and without keyboard. So that is true.
A physical keyboard for the iPad has been around since day-1 of gen 1. And yet, there aren't any apps that REQUIRE a physical keyboard... there are no apps that depend upon key combinations for keys that don't exist on the onscreen keyboard. Android apps never required mice.
That's true!
You assume that it is a technical reason why Apple hasn't included support for mice. It's not. It is a marketing and design decision. Adding mice (and universally accessible file system) would pretty much snuff out segments of the Macbook (Pro and non-Pro) lineup. THAT is perhaps the primary reason.
Agree with you there. Apple's reason to not include mouse support is primarily money and marketing. iPad users have technical concerns, but I really do not think that Apple has even thought about the technical side effects on such solution. It's because they simply do not want to do it.
In other words I see iPad users' concerns because not everyone can imagine how mouse support would work with iOS but I do not think that this is what stops Apple. Apple just does not want to do it.