I think there are different reasons why that may happen - perhaps a misconception of the problem space and what an off the shelf tool provides, or misestimation

I think there are different reasons why that may happen - perhaps a misconception of the problem space and what an off the shelf tool provides, or misestimation of implementation time vs learning time. I don't think it is appropriate to say that developers don't value their time and therefore need managers, as a blanket statement.