1. Edge cases. Chances are you do not need to cover every edge case, at least when building an MVP. It can take more time to learn a complex API than to build in house. See also premature optimization.
2. Someone else maintains it. In the event you decide to use someone's dependency and they decide to unpublish it with the click of a button.... (ok at least this one has been fixed, but API versioning can still be a bear).
1. Edge cases. Chances are you do not need to cover every edge case, at least when building an MVP. It can take more time to learn a complex API than to build in house. See also premature optimization.
2. Someone else maintains it. In the event you decide to use someone's dependency and they decide to unpublish it with the click of a button.... (ok at least this one has been fixed, but API versioning can still be a bear).