I can buy programming time from others who will solve the unique part, too. I don't imagine I'm somehow the only person in the world who can solve some particular problem.
I can even buy time from people who will develop the description of the problem well enough from my wague idea to make it comprehesible/implementable by programmers, and who will lead those programmers for me.
My point is that it's not important whether something is common or unique to my product. For some "rolling their own" even if it's a common solution may be a good and comparatively cheeper proposition, if that will end up costing less as a result and will leave more resources to devote to their product overall.