system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do apps like Instagram and Vine make money without ads?
gpt
Some apps aren't paid or display adds because their objective is to create a vast pool of users. Note that with no advertisement or fee, users have less inertia to adopt the service. When the number of users is vast and accepted as a "must have" app, the producer starts to study ways to generate income or intends to sell it.

Is a comum business model for app makers: make it, growth it, sell it.