I'm pretty sure one of the most complicated things is preventing automation of content - bots. which would be an arms race type condition. Bots you want to prevent - people not using twitter's api to do their bot stuff. Why would people not use twitter's api?

1. who would trust twitter not to change API and make code worthless

2. people who want to do stuff Twitter doesn't want you to do in an automated fashion.

a bunch of people I talk to say it is massively complex but typically fail to explain how, especially given the super-glacial pace at which they added new features for 15 years. And yes, this article kind of doesn't disprove the bloat at all, unless every single SRE quit? but that is also not what's stated in there.

I imagine the infrastructure implemented is fairly complex, this post does outline that it's not a super simple operation. It also alludes to there being more business units than just the core application.

Even "simple" things become complex when they need to scale to billions of users around the world, handle a high rate of traffic, deal professionally and legally with all the different jurisdictions they operate in and all the advertisers they serve, etc.