They are certainly still trying. I used vscode a while ago. Some of the best and most essential extensions like LiveShare and Remote are proprietary and worked only on the proprietary build of vscode (the last time I checked) and wouldn't work on OSS builds like vscodium (why though?). Both these extensions and the proprietary build of vscode come with telemetry that's either opt-out or always enabled. They nudge you ever so slightly and gradually towards the proprietary build. I left vscode since I don't like such manipulations.

It's not lock-in, it's feature differentiation. Other platforms are free to develop their alternatives of these plugins. There's nothing preventing the community to develop a fully OSS Liveshare or Remote extension (and they are!)

but there is. VSCode core may be open source, but the plugin marketplace certainly isn't. So if you for example use VSCodium, you don't have access to the plugin marketplace and eather have to use an alternative or manage your plugins completely manually on the filesystem.

So what? You use the plugins available on the platform you use, that's standard practice. Would you complain Sublime Text plugins are not available on VSCode? Or emacs plugins are not available on vim?

This is not lock-in, just a different feature set.