[cdavid]

You had to accept some license terms before you could download the VST SDK. When linux audio started to get "serious" 20 years ago, it was a commonly discussed pain point.

Concretely, it made distributing OSS VST plugins a pain. Especially for Linux which generally will want to build their packages.

[TonyTrapp]

Note that his was the VST2 era. VST3 was commercial license or GPL 3, which was an improvement, but only slightly, because it excluded open-source software released under the GPL 2, and also MIT/BSD/whatever-licensed software couldn't use it (without effectively turning the whole software into GPL-licensed software).