I’d love it if IoT devices could store data in my own encrypted storage (S3, sftp, whatever); then give me apps to see my usage reports and stuff. Why must everything be controlled by whoever I buy the hardware from?
Because they can, and they don't give a fuck whether you like it or not. Compare yesterday's article, "I Pay for News; Why Do I Still See Intrusive Ads?"[0].
There is some merit to argument that "non-techies can't manage their infrastructure", but I question its general validity. For one, an IoT device or a companion box can serve as a local endpoint, things don't have to go into the cloud. For two, a configurable device using open APIs could enable community-level support. I.e. my mother won't be able to set up a server for her smart thermostat data, but I can do that for her, and for her neighbours.
Alas, most IoT equipment is sold as loss leader, meant to lock you into whatever bullshit "platform" the vendor is pushing, and to hold your data hostage. Personally, I avoid IoT because of that - companies are just disrespectful. The design of their products is one big middle finger in the face of the potential customers.
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I wish there were more IoT style systems that cared about privacy and portability.
The furthest you could go is something like an app that reads data on the free icloud / google drive allotment they have. Then you'll have to deal with instances of losing their password / changing their broken devices / etc and all the lock out situations that happen.
You start to say fuck it and provide your own backend and now you're back at status quo.
I understand they mostly do it “because they can”, but that was the same reason that cell carriers locked down phones & controller the installed software pre-iPhone. There is precedent, and thus hope, to break this logjam.