Actually it is all about piracy and absolutely 0% due to some random conspiracy theory you are floating around. Safari and Edge have better OS level integration preventing piracy so streaming sites allow you to watch content in those browsers at a higher quality. Google has all the bargaining power in the world, they could easily comply but they just don't or are very slow to do so.
Can you get us any source for this? Because it makes 0 sense.
Let's assume all you saying is true, then;
– why we're able to stream pirated media normally through Edge and Safari?
– why isn't Netflix limiting 720p and 1080p content as well?
– why is Netflix the only streaming service that limits quality depending on browser used?
I have no doubt that hardware DRM has better protection, but if protection is really in question, it would make sense to apply it to all resolutions not just one.