[withinboredom]

When it costs less to spend a years worth of salary building it vs. paying for it.

At a company, we would stick a team of up to 3 devs + manager on an internal product to replace or create something we wanted but didn't want to pay for. That cost is R&D (so taxed differently -- ammortized) so it would often be magnitudes in less cost than paying for a product, unless the product did something we conceivably couldn't build or only a small number of users would be using (such as on-premises BI tools).