I think you have some of your story slightly wrong. There were two previous build systems before Cargo; both of the authors did leave Rust, for different reasons. I'm guessing you are talking about the second. I don't remember the exact details, and I thought that they left a year before cargo was announced...maybe I have rose-colored glasses.

But with green threads, Rust had them for quite a while, on the order of years. I think the person you're talking about was in favor of the removal of green threads, which we were initially against, but it did end up happening. That person also left Rust but wasn't banned; we've only ever banned one person, and that was fairly recently, and it was for an extended harassment campaign, not over some sort of technical disagreement.

> So this big community led approach is more of practical matter than some enlightened way to develop software.

We believe that it produces better technical outcomes. Rust has more paid developers than many, many languages. Regardless, when making decisions, it's important to be informed, and there's no better way to be informed than to get a broad description of the problem space and other approaches to solving them. One person is never going to be able to be an expert in everything that a language needs.

There's also sustainability concerns with BDFLs, but that's a larger topic.