> On the other hand, the goal is also to increase the vendor lock-in, by providing everything inside their garden walls, so that people keep going further into giving up any side channel and into putting all their eggs into the same Github basket.
That's also true but where do you draw the line with vendor lock-in and convenience?
If you use Google's mailing list service then you're locked into Google. What if they decide to drop that like many other services in the past?
If you use a self hosted forum / mailing list instead, the repo owner is on the hook for setting up and configuring a server along with potentially registering a domain name just for that aspect of an open source repo. With something like Discourse that could be like $20 / month + domain just for 1 instance of it.
If you decide to use Discord or Slack as a side channel for casual chatting or feature requests then you're locked in there too and there's no persistence (at least not with Slack) or SEO discoverability.
That and with any of the above solutions chances are folks will end up reporting bugs in those side channels which means someone needs to go back and write them up as proper issues, often times that'll be the repo owner. Plus now all users need to jump through hoops by registering on those external platforms to give a feature request on a project on GitHub.
I hate the idea of vendor lock-in but at some point integrated platforms make sense because the alternative is worse. As a developer I really like having my code, CI, issues and a place to chat all in 1 spot. If GitHub dies, that's fine there's always Gitlab. If Gitlab dies, there's always Bitbucket but at this point the developer community would likely revolt and come up with a new solution.