For anyone frustrated by this, you can download .vsix files from this site:
VSIX Downloader (source).
You just have to rename from .VSIXPackage to .vsix and you can use CTRL-SHIFT-P, then find Extensions: Install from VSIX... and you can install manually.
Auto Updating probably won’t work, but it’s a decent workaround, if you’re struggling with finding anything usable in OpenVSX.