WHY is this still the case? I mean, Bluetooth is fundamentally just a communications protocol broadcast with some kind of antenna. Yet I don't have these kinds of issues making wifi or cell service work.

Who decided to use such a flaky protocol for audio and such, and then remove the reliable connection?

The problem with Bluetooth is the stack is too complex. Too many application-specific profiles baked directly into the protocol, which in turn need to be dealt with by device manufacturers. Bluetooth basically handles everything from OSI Layer 1 through 6 at the same time. See: https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles

Add to that great complexity at Layer 1, and constantly changing specs. Bluetooth 1, 2, and 4 are all radically different than each other.

Compare with WiFi, which only has to do one thing (Layer 1-2). Cellular is much more complex, but that's why releasing a new phone involves endless rounds of (usually mandatory and very strict) carrier certification.

The RJ-45 connector is an open standard that can carry basically anything—internet, video, audio, low-level data, etc—at a high bandwidth and with low latency. Why can't we have a wireless standard that does that?

I want non crappy Bluetooth mice that don't require a separate USB dongle. :(

Edit: To be clear, I'm sure ethernet cables are an entirely different thing and there's actually a very good reason why wireless makes everything more complicated. But, well, maybe that's one of the reasons people would like to stick with wires.

It’s like many things designed by committee of stakeholders with very different needs.

Everyone gets what they want, except for the end user!