I don't really see how one leads to another, could you elaborate? Looking at these protocols, it seems to me that later versions of HTTP attempt to address errors resulting from the overly simplistic design of HTTP/1.1.

That's a pretty silly take. You're basically asserting that implementation difficulty is always the main priority, and there can never be any worthwhile tradeoffs that could offset that complexity.

But in reality, the world probably only needs a few dozen H3 implementations, just like there are only tens of production TCP stacks. But those implementations will be used by billions of people, hundreds of billions of machines, and handle effectively all data transmission of the entire humanity.

The leverage is massive, even the most minor improvements will be able to pay off any level of engineering effort.

Enter IPv6. Same arguments, it's 'only' a matter of implementation. 30 years later still most of the implementations are worse than IPv4.

At least IPv6 is reasonably scaled for our world which IPv4 was never meant to be (The abomination of NAT).

TLS is more costly to implement than simply not encrypting or signing anything.

Sometimes cost of implementation isn't the only consideration.

We should have stayed in Gopher.

Even HTTP1.0 is fairly enough and dead simple to implement.

Usually, just a bunch of planned obsolescence fan boys.