This is totally different use case, you may prefer GTK or Qt if you know it, tauri is about giving the power to web devs to compete with Qt devs.
What has been stopping them? PWAs have been around for quite some time.
It's just take time and browser feature complete, like photoshop is one web now.
I looked at it, but there is very little ecosystem support for other UIs beyond Material. There are partial Macos/Windows (fluent) libs but everything still seems quite immature. I do think it gets better rapidly though.