Some features require Secure Context. Browsers just don't enable those features in a context that isn't secure (HTTP is only considered "secure" on the loopback network to your own machine). If it's a Javascript API it returns an error, if it's an HTML or HTTP feature it doesn't work. "Here's a nickel kid, get yourself a secure context".

Both Chrome / Chromium and Firefox have explicitly set policy that new features (as opposed to tidier ways to do things that already exist like DOM improvements) will require Secure Context, and there's already a weak assumption that even some tidying up will go into secure context when the rationale for not doing so is shaky (e.g. some of the web crypto features that needn't technically require Secure Context do anyway).

Because the alternative is to embed a TLS private key that would allow you to MITM every other one of those devices. Someone extracted it? Looks like you have to either (a) bury your head in the sand or (b) rollout an expensive recall to change certs on those devices.

Why use slightly compromised HTTPS versus plaintext HTTP? Same reason they have those super cheap locks on diaries from the 90s: it's a deterrent. Makes it a little harder to do a bad thing.