- Low barriers of market entrance
- a competitor with a plan (copy and paste functionalities), much bigger resources and a longer learning-curve behind it plus
- probably a lack of planning at Snapchat in case someone fitting the description under 2. making use of the fact under 1.
From the viewpoint of business and economic theory they did not stand a chance. Which does not mean, that they could not beat the odds even now. But doing so is hard, especially if you are totally contestable and have a relatively tiny user base.
Look where Microsoft took Skype to and how Google faired with Hangouts. Both surely got resources with a long learning curve but evidently no plan. Even Apps LINE and VIBER seem to struggle these days, despite their size.
Consolidation in the market is inevitable because a user can only use a limited number of Apps per day! That is where WeChat steps in! If someone is stoned enough to value Snapchat at 20 billion USD, you realistically got to rank the Chinese as a 20 trillion venture!