- A large chunk of the world (especially people in developing countries) will be unwilling to pay anything more than $0.
- Even if they want to pay, most of those users won't have a payment method set up. How many of their 2 billion+ users have a credit card or even a bank account?
Not sure where you got that number, but in 2013 (before aquisition) they reported ~$10 million in revenue. (https://www.sec.gov/Archives/edgar/data/1326801/000132680114...)
They brought in $15 million in the first half of 2014. (https://www.sec.gov/Archives/edgar/data/1326801/000132680114...)
They only had 55 employees at acquisition.
They might not have become a unicorn... but there most definitely was a path to profitability.