I wasn't really commenting why the national TV's have to follow ancient standards.

I was commenting why private people think they have to follow those 50Hz standards too. And I gave examples of all the technology that they have around today that doesn't follow a 50Hz standard. And yes, that include the digital TV's too. They can do easily 60Hz, even if the box says they are compatible with the national 50Hz TV.
When you watch YouTube or whatever other smart apps that provide video streaming, on a smart TV, it does it at 60Hz.

We are digressing, but the discussion is interesting . . .
Not everyone has a smart TV. In fact the dumb ones with muliptle input ports are still a majority use (see my commnetary about Tv life in flat screen technology above) . . . which is giving rise to a market for smart set-top boxes that connect to the internet to use with those dumb TV's, just like (years ago) there was for a set-top box for digital broadcast to use with an analogue TV. In the downunder land, that's foxtel and fetch, which enable all the Tv channels plus pay Tv and sometimes streaming like stan and netflix. In time (10 years+??) as smart TV's dominate, that market too will pass . . .

Why that long? those Tv's - smart is pretty much also large - are not cheap (down here, my not-smart FHD 42inch OLED Tv with 3hdmi, 3 usb rgb and digital radio inputs, cost nearly $900 8 years ago. Cost has come down, but then theres' 4k now so it's not as great a reduction as you might think. And the the screens are getting bigger. Not so long ago these were mutli-thousands of dollars). Usually replaced only as the old one breaks or a household trades up to a bigger house with hometheatre.

But IMHO most users that watch Youtube do so on a computer/browser combination. The YT formats are setup for fast download, using a browser, and despite that being nominally .mp4 now, mp4 is just a container; achieving fast downoad sacrifices resolution to speed. It's not really established for playing on a large FHD TV screen, however connected.