Is this just due to the fact that Netflix will only send 720p to a Linux PC running chrome?

I assume the parent was ironic since 4K/Dolby Vision versions of top Netflix shows are actually released by pirates on the very day they are available on the platform.

No, they're not. It's actually quite rare for that to happen.

Nobody uploaded Stranger Things S4 in UHD until after the season had finished for example.

That fact is directly due to the above, not the other way around.

And it's holding up content against real customers for years.