https://old.reddit.com/r/programming/comments/6xh3xp/reddits_main_code_is_no_longer_opensource/

Here's a good discussion on it. Here's a great comment from a deleted account:

"back in 2008, Reddit Inc was a ragtag organization1 and the future of the company was very uncertain. We wanted to make sure the community could keep the site alive should the company go under and making the code available was the logical thing to do"

Translation: We needed you guys back then. We don't now.

The rest of it seems like a combination of technical hurdles that don't seem particularly compelling (they don't need to have secret new feature branches in their public repo) and some that don't make any sense (how does a move away from a monolithic repo into microservices change anything?) and some that are comical (our shit's so complicated to deploy and use that you can't use it anyway)

It's sad that their development processes have effectively resulted in administrative reasons they can't do it. I remember them doing shenanigans like using their single-point-of-failure production RabbitMQ server to run the untested April fools thing this year (r/place) and in doing so almost brought everything down. So I'm not surprised that there doesn't seem to be much maturity in the operations and development processes over there.

To be fair though, the reddit codebase always had a reputation for being such a pain that it wasn't really useful for much. Thankfully, their more niche open source contributions, while not particularly polished and documented, might end up being more useful than the original reddit repo. I know I've been meaning to look into the Websocket one.