Many organizations don’t use or want to use git. This is another convoluted solution, trying to fit a square peg in round hole.

Another reason not to use sourcegraph is it’s proprietary (with some open source parts), unlike opengrok fully open source.

Is the sourcegraph "open core" unlike how redis is "open core", eg. The main code is open but there are paid, closed-source modules and extensions?

Sourcegraph is open core like how GitLab and VS Code are open core. You can run "Sourcegraph OSS" and get limited features, or you can run Sourcegraph (see https://docs.sourcegraph.com/#quickstart) and get all the features, but you need a license key when you hit the user limit.