Bit late here, but I'll give my opinionated answer anyways. The public sector is overall of lower human employee quality than the private sector. A high quality person that wants to get something done without a ton of red tape just doesn't stay in government work for the most part. It's not salary related or even money related, it's accountability related. Fixing that requires firing many entrenched people which will not happen. This is why many successful governments in the US task the private sector with building, maintaining, and sometimes even managing these projects. That has problems too, but in many cases at least it's done in reasonable time with reasonable quality or there is someone to hang.

Oh and I should mention large seemingly-private orgs that win all contracts, especially that are highly unionized without competition, are essentially government orgs and suffer the same issues.