Why are sub-optimal computer languages the most popular in the world?

When PHP came out it was a big hit because of deployability. Cheap web hosts could install it and hack out quick scripts, or more important, install WordPress.

There were a few subtle points in how it was built that meant you could write bad scripts and not crash the server. There were commercial alternatives, some pretty spiffy, but they were expensive and risky (you could test PHP for yourself or you go up the chain of command to pay $5000 for a Cold Fusion license then be stuck with it if you don't like it.)

Other communities working on blub languages thought that the good properties of PHP were not important. They might have been minimal but they were not viable.

For JavaScript, the answer is pretty obvious: there simply weren't (and still aren't, really) any alternatives.

For Python, it's really a phenomenon of trends. It's got all the right pieces (easy to learn and use, good community, good library ecosystem), but lots of languages have that. Like so many other things... It became more popular because it was popular.

Runtime performance is only one factor in the programming language game. Many other equally important factors are purely emotional. We are human, after all.

Because for the vast majority of purposes, ease of developer use far outweighs performance.

Also, JavaScript has long had a monopoly on the worlds most popular deployment platform.

No language is optimal in every dimension. Choosing a language is choosing (subjectively as well as objectively) which dimensions you care about.

What do you mean by term "sub-optimal"?