Users want an installer. You can see what the installers are doing by looking at the scripts in the repo (this is an open source project). Admin permission is necessary to write to the Global VST folder. You can direct your "Wow" at Steinberg if you want. The spec was recently updated to allow for a User install location which has been considered: https://steinbergmedia.github.io/vst3_dev_portal/pages/Techn...

If you don't want an installer, you can download the pluginsonly bundle on the release page and do it yourself: https://github.com/surge-synthesizer/releases-xt/releases