Problem is that there’s little incentive for them to do so. They each have their own small markets which are generally married with local karting businesses. They rely on each other to survive, so they do what’s best for them.
In WA… you know how that goes 
Now don’t get me wrong, I’m not saying it doesn’t suck.
The only way you can get close to uniformity is to offer an incentive of some sort to racers and tracks. This is why the Briggs 206 has done so well.
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The simplicity appeals to new and existing racers, especially with how people value their time these days.
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It’s not super fast so you can have newcomers drive it and have fun right away.
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The parity (always relative of course) is pretty good.
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It has marketing and a brand behind it, including prizes and benefits for racers and tracks. Also the prizes
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go beyond just awarding the winners of racers.
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The rulebook and tech make it easy for tracks to implement.
You need all of these for widespread adoption.