It’s also worth noting that Facebook had made acquisition offers to Snapchat at the end of 2013, around the time Snap Stories went live. SnapChat’s rejection of Facebook’s offer (which was around $3 billion) was widely publicized and many had seen some arrogance to it. I’m sure that was a pivotal moment for FB; if they couldn’t acquire their competitor, then they would do everything they could to steal their market/mindshare by replicating them. The more similar your competitor is to you, the higher the chances that the bigger one will win.
If Snapchat had been a bit more astute, they would’ve picked up on the fact that FB might have done what they did, and they would’ve relentlessly kept up the pace of innovation in order to differentiate themselves more and more from FB. However, their biggest next innovation was arguably SnapChat Spectacles and that was in 2016, a full 3 years later. A lifetime in this cutthroat market.