Probably the reason Vs Code has so many extensions, is that they can easily (low barrier of entry) be created in JavaScript. This is mainly due to the fact that VS Code is an electron application, itself written in JavaScript.

It sucks for zed, because these extensions allow users to customize their workflows to their needs which decreases their liklihood to switch to a different editer. I think the message of the post is that VS Code's large and mature extension ecosystem will somewhat impede users migrating to zed.

The irony in this is that the people behind zed and atom were the ones who initially created electron for atom.