Broadly, the private sector is skills ability led. The more productive, highly skilled you are, the more you are paid. Obviously supply and demand have a heavy influence - just try getting skilled sw people with 10+ years.
In my experience, the CS is based purely on years worked for CS and sizeof teams. Theres limited skills or supply and demand.
Id guess there wasnt an issue when CS and private sector operated by throwing people at problems. But thats not been the case since the early 90s recessiom, which saw the middle management made redundant.
Now you have the ridiculous issue of contractors doing the core work and the CS building pointless little empires.