Not hating on SVN, just think the “why aren’t they using a more modern/superior X” should be taken in that context.
>why aren’t they using a more modern/superior X
Because no one cares if it's not superior for that case.
The line you quoted, I had in quotation marks because it was essentially the question of the parent thread, not because it was my stance.
"That context" meant that they started with tools like SVN for version control, and Facebook for their community. They were 'current' at the time and they probably haven't seen a reason to switch.
I have no problem with this. I use many tools people find uncool or outdated. I still use RCS in places and like it better for those particular use cases (eg Bind DNS zone files), where things like file locking and versioning files vs codebases are features and not detriments. I have shell scripts I've carried around for 10-15 years to support it (ironically kept in git now), and I don't feel like reengineering for a git/ci workflow to get back to feature parity.
You should look into the history of RCS->CVS->SVN (and revision control systems in general) to understand the nuances there.