It's likely companies like Microsoft (pre-Surface), peripheral manufacturers (eg, Logitech) and motherboard manufacturers (eg, Gigabyte) would have gladly got on board in that era.
It's likely too late to start this in 2019 (but I may be wrong). Certainly the late-1990s would have been the ideal time for this.
In a way, this is much like the situation with desktops-- Dell and HP was/is big enough to come up with their own custom mainboards and cases, but most smaller shops are going to go ATX.
I suspect part of the reason we didn't see much laptop standardization was that the second-tier manufacturers are weaker in the laptop sector than desktop, as well as being weaker as a whole than they were in 2000 when ATX was becoming a thing.
Outside of a few narrow gaming and workstation niches, there are few use cases where you can't find a suitable big-brand laptop, so the second-tier brands (and the manufacturers that supply them) are in a position of fighting for scraps, not one where they can start promoting the benefits of standardization.
This is likely worsened by the mindset that laptops are unupgradeable-- people bought ATX desktops figuring they'd buy new mainboards in 3 years, but generally assume the laptop is going to be stuck in place.
The reason it hasnt happened in laptops is you would have to compromise size and form