While you could do that, the hub needed to implement the logic to actually convert the different "APIs" that the products spoke. E.g. imagine an IKEA remote sends "button_on" to turn on the light, but the Philips remotes send "light_on" or something. Philips lights will work with their remotes but not with IKEA remotes, since they wouldn't know what to do with "button_on". Zigbee2mqtt and ZHA are great projects that implement a compatibility layer to all of this, but they do have to explicitly support every device (and they support basically _every_ device there is, thanks to a ton of community work, they're genuinely great projects and something that wouldn't really be possible without open source). You mention that you can pair between different vendor's products, but that's not quite the case - you can pair different vendor's products to the hub, and the hub can translate between them. But while you can pair an IKEA remote to an IKEA bulb without a hub, you can't really do that between different brands.
Matter simplifies this. It defines the API layer. You can use Thread without Matter, at which point you basically have Zigbee + IPv6, but the power comes with Matter since now every device is speaking the same language and can actually understand each other.
> Matter simplifies this. It defines the API layer.
Technically Zigbee _also_ defines an API layer -- the Zigbee Cluster Library, or ZCL -- but that's more like an opt-in standard you _could_ implement, rather than any hard requirement. And no surprise, the Matter Cluster Library Specification, being authored by the same CSA that made ZCL, is eerily similar to ZCL...
But as I understand it, you're right that Matter is essentially "hey everyone, let's _actually_ standardize around a common application layer". It isn't technologically revolutionary (the building blocks have been around for more than a decade), but it's a better packaging of it all.
Source: My employer has been involved with Zigbee and other low-power network technologies for a long time.
> you can pair different vendor's products to the hub, and the hub can translate between them. But while you can pair an IKEA remote to an IKEA bulb without a hub, you can't really do that between different brands.
Yes you can, I did that with Ikea, Philips and Innr brands. No hub, not even Z2M involved. Yes, as you say they do need to agree on a "protocol" and AFAIK they are all following Philips lead on that, but they can totally work in a P2P fashion without any hub. They negotiate their own key, you just need to pair them with a very close distance (less than 5cm approx).
Thanks, I didn't know that this worked! I guess this is more of an informal standard that they ended up following Philips' lead on, but still, better to have this kind of thing be officially defined.
Matter simplifies this. It defines the API layer. You can use Thread without Matter, at which point you basically have Zigbee + IPv6, but the power comes with Matter since now every device is speaking the same language and can actually understand each other.