In principle, the answer is getting together and standardizing on generic protocols.
Unfortunately, there are multiple reasons why this can't happen in the current environment.
The business reason is that all the big tech giants are now deeply accustomed to lockin-as-a-model, and you can't have lockin if you have a standard that everyone can use equally. So, literally everyone in the space sees it as their incentive to let other players conform to their standards, but not to conform to anyone else's standards. This does not result in a standard, de facto or de jure.
(I made the same objection to the "metaverse" concept a couple of weeks ago. It can't work as some people are envisioning; the business proposition at this point is complete nonsense. Every participating company will be happy for other companies to voluntarily walk into their walled garden, but no company is going to walk into somebody else's walled garden.)
The technical reason is that any attempt to standardize at this point is more likely to produce a mess like bluetooth than any sort of coherent standard. Plus you get an echoing of the business model problem where every participant will see the standard as a weapon to be fired at their competitor rather than something to conform to for mutual advantage.
Not helping any of this is the problem that the problems that they are solving just aren't that compelling. This limits the amount of value they can extract from me by virtue of the fact I'm not paying for more than I'm getting from the 'smart home', which doesn't really leave them with much money to play with. It also doesn't help that the camel's nose is already under the tent in terms of not simply enabling the user but trying to control the user, with things like letting this authority twiddle with my air conditioner and that authority twiddle with my hot water heater, and in 2021, I have less than no confidence that buying into a smart home won't continue this trend.
Personally, my assessment is that the tech industry of the 2010s and the 2020s is structurally and temperamentally incapable of producing a high-quality smart home. The best they can do is create a locked-in walled garden that works great if you buy into it from top to bottom (and pay the subscription fees!), but gets abandoned in three to five years and then becomes totally nonfunctional as they pursue the next thing.