Most languages including C and C++, had leading closed source implementations, that is why being standardised by ISO mattered.

But standardization also matters for avoiding vendor lock-in, right?

Like, Python and Javascript both have many "implementations", and those are some of the most popular languages. Python does not have an ISO specification. But Javascript does have an Ecma standard, ECMAScript.

Rust is getting another implementation in the form of gccrs. And there is work on a specification for Rust https://rustfoundation.org/media/ferrous-systems-donates-fer... . Arguably not a standard, but still helpful.