There are two parts to this. First, in the United States we tend to not have universal standardization on anything except basic safety. There are a lot of market reasons for that. Chargers are the classic example. people have been complaining for 20 years about having to have different charging cords for different devices, but there’s still no universal standard. 
For the second part, the companies do know that customers would like this. So some companies are working on creating at least a popular standard, if not a universal one. See
Matter - smart home connectivity standard (formerly Project CHIP)
How far they will get is anybody’s guess right now, we will just have to wait and see what happens. Although they’ve definitely got the right mix of companies involved. But that’s still a ways in the future.
But for now, low cost home automation really only offers three types of systems:
Type 1: very limited device selection
Security companies do it the simple way: they pick a very specific set of devices, say “we work with these“ and that’s it. Usually there’s only one or two choices in each device class. Their customers may feel restricted, but they aren’t confused.
Xioami does this in home automation. If you’re OK having your cloud account hosted in China, you don’t need more than 30 devices, and you’re willing to only buy their brand, the gateway is a strong candidate. For somebody who lives in an apartment in Beijing or even Hong Kong, it’s justifiably One of the most popular systems.
So it’s a good example of how a single company might do a home automation system very similar to the low cost home security systems currently available. Again, customers might feel restricted By the limited selection, but they won’t be confused.
https://www.gearbest.com/living-appliances/pp_344667.html
Type 2: a logo program with very strict standards
Apple does it by very strictly enforcing a unified standard for HomeKit accessories. Devices that work with their platform have the HomeKit logo on the box, so it’s pretty simple. There are more choices then there would be for most of the security systems, but still not a lot and most of them are in the higher cost range.
It’s a good simple reliable home automation platform that runs locally except for voice control and it’s justifiably popular with those who already have iOS devices. But of course it doesn’t help anybody who uses Android or who wants a wider range of choices or just more complex automation rules.
Type 3: the model number matters
And then there’s SmartThings, Amazon Echo, Homeseer and others that operate by publishing a set of standards, opening up some integration, but not really enforcing much and leaving it up to the individual device manufacturers to create the integrations. The end result is what you see. Lots of choices, lots of customer confusion about what works and what doesn’t. Many people find benefit in having those choices, but it does require doing some homework when you are considering new devices for your system. Whether that much work is worth the payoff is an individual assessment.
