This is easy to explain when you treat third parties as liabilities as well. For many companies this is a bigger liability than maintaining the code in house.

I recently made the decision to have a third party build a component as opposed to doing it in house. The cost and time to build a component in house vs using a third party ended up being a wash, but the third party offered to maintain and support a solution so this presented less risk to us. This major risk we incurred was in vendor lock-in.

These types of trade offs happen all the time. Think about virtually any SAAS offering that could otherwise be built in house.