Installing app from any source is not outrageous, I use it for my Pioneer receiver who would otherwise have no remote, I use it for my paragliding variometer. And I could use it for anything else I chose to, since I am free to decide. The list of what I can do with similar other devices but can't do with the most expensive of them is quite long. This is not expert level, experienced beginner at best (not for Apple products obviously since jailbreaking is advanced topic).
Due to above also being 100% stuck with only Apple payment system which takes 30% all the time vs having the freedom to choose. This can't be more un-american (at least to ideal, reality is another topic).
Life for others does not need to conform to your ideal - that goes both ways. Closed vs open systems to 'hackers' have a special meaning to many people here on this forum. And yes these topics are exhausting to us all, explaining ad nauseum why more freedom is better for users especially long term, and why Apple et al desperately don't want users to have it.