To most, driving is the top job. Few look at progressing their careers. Some do go into management so perhaps become instructor drivers then driver managers and perhaps look to going into training or operations management whilst keeping their key but those jobs often arnt exactly a promotion.
Some drivers with an interest in the job may look at intercity TOCs, I know a few drivers who have gone to east coast as they wanted to sign HSTs but for the vast majority being a driver is good enough and with the money, job security, work/life balance, available overtime and final salary pension many see no reason to risk promotion.