You can. There are simple options, that only recognise predefined sentences, that even work on a Raspberry Pi, and at the other end of the spectrum you can host an LLM locally and chat with that if you have the right hardware (Coral isn't powerful enough for that, you want a GPU with lots of VRAM). Obviously setting this up is more complicated, but there are a lot of options to do it your way.

IIRC it's supposed to be getting better rapidly, as it's an active focus of development for Home Assistant.

That said, I thought this seemed like a good guide on how to set it up as of 8 months ago. (I'm not necessarily a fan of that guy's bombastic over-enthusiasm, but the info seems good.)

For music, it's not great. For voice, it's pretty good. It's decently loud and legible. There's no bass. The mics however are pretty good. As far as I've read, you can't get the mics to work well unless they're tuned for that speaker in physical placement and hardware/firmware. The HA speaker uses the same kind of DSP chip that makes it possible for it to hear well in worse than ideal conditions which makes speech recognition work so well. So yeah, if you don't wanna faff with stuff and you don't care about music, just get it. It's got 3.5mm TRS out if you wanna hook a proper speaker for music. The DAC is probably not amazing for HiFi but should you want to hook up something like a JBL Charge, I imagine it should work. In fact I'm planning to do this in another room where I used to use a larger Google Nest speaker for music.

Because software is hard to write and not many people want to spend their free time writing it???

Instead of complaining, Go be the change you want. It's all open source...