Earlier quoted context omitted.
It is not "virtually closed source" to license something as GPLv3 and also under a proprietary license. In fact, it is something explicitly advocated for by Richard Stallman himself and the Free Software Foundation generally: https://www.fsf.org/blogs/rms/selling-exceptions He's got mixed feelings, but says "I consider selling exceptions an acceptable thing for a company to do, and I will suggest it where appropriate…
There is a subtle but important difference here though: If you publish a piece of software under two licenses, one open source and one commercial, why would anybody pick the commercial one? You cannot say "corporations have to pick the commercial one". The only way to do that would be to include a term in the open source license so it cannot be used by corporations. But then it would no longer meet the open source de…
The OpenSource license is typically GPLv3 that imposes that your whole application has to be GPLv3. This is enough for corporations to avoid it.