The nice part about mqtt is other things can subscribe to the same stream. I've also seen people do some really interesting things with hosting a copy of HA in the cloud -- this is what they connect to while outside their network -- and using mqtt to push updates to a local HA.
Okay but if you have Home Assistant in the center of all things, why would other things need to subscribe to that same stream?
I use MQTT but for me it's only a tool for getting a certain device integrated in HA. I don't see why I would want more devices to communicate that way.
Plus, from my development background, I have grown to really dislike event buses. And mqtt sure feels like a weird big non-strict event bus with some persistence.
Because HA is a single point of failure. It's big, complex, and frequently updated (there were 3 minor version updates this month already.) Any one of those updates could bring some issues that require fixes/rollback, and even when it's smooth, it takes a minute or two on my 8th-gen, i5-based, NVMe-having home server, not some underpowered Pi or SBC.
Meanwhile, a standalone MQTT broker like Mosquitto is rock solid, had 2 minor updates this year, and could run on the most minimal of hardware/LXC.
