Having taken part in many build-vs-buy decisions, there are no easy answers. The overriding factors in most decision relate to the specifics of the business. Some very common reason for buy decisions:

- You don't actually know if this feature will be important long term

- You have many urgent needs, the opportunity cost of waiting for "build" to finish is too high

- Your company is, for various reasons, unable to attract and retain the kind of talent who could maintain a system of this complexity (I realize this sounds like "we're not willing to pay market reates", I promise it's more complicated than that)