The way I remember it, Facebook came along while MySpace and Friendster were still large, strong companies considered to have significant market share. Friendster wasn’t growing as fast as MySpace by that stage but it was still big. And there was Orkut too.
What killed them wasn’t timing. What killed them was that some markets (eg social media) tend naturally towards a monopoly over time. Most people (and I’m thinking “most people outside of Silicon Valley” when I say this) don’t really want to be on multiple social networks. Once one social network starts to grow faster than the others, users on that product convert more users over from what they were using before, especially if they get access to features their previous choice of product didn’t offer.
Friendster ran into massive platform scaling problems and then hit big leadership instability as the board tried to build a better management team, so that Friendster stopped improving right when Facebook was hitting peak “move fast and break things” stage and offering new features almost every day you logged in anew.
MySpace misunderstood the psychology of social networks, over-investing in features to help us customise and publish on our MySpace page. Right when Facebook was doing a great job of helping you recruit your friends and connect with you on Facebook, MySpace was underinvesting in features to help us connect with real-world friends on MySpace. You were more likely to connect to complete strangers than actual friends on MySpace.
Facebook’s execution wasn’t flawless – it nearly lost the lead in social networks by underinvesting in native mobile support around 2007–2010 as smartphones meant that customers demanded to be connected to Facebook and nurturing these new online relationships with real-world friends when they were out and about. But in an open admission he’d got it wrong, Mark Zuckerberg managed to redirect the company’s now-significant engineering resources towards building the best mobile social apps and salvaged its lead.
The social network startups hit by poor timing were the mobile-native social network products like Twitter, Path, Instagram, BluePulse and now Snapchat. If they’d had Facebook’s opportunity to largely replicate the Western world’s real-world relationships on a desktop platform before smartphones became a thing, maybe they could have stopped Facebook eating their lunch. But in each case Facebook has been able to acquire or copy the key features of mobile-native competitors using the revenue engine of its desktop display media business to soak up the cost of out-competing.