Permanent members of staff seldom get the same money as skilled contractors and have to put up with a lot more restrictions around holiday and work life balance.
I would equate a contractor in the UK to being the equivalent experience of being a consultant without the politics and drama that comes with it. I have worked for almost a decade as a consultant in different countries and much prefer being a contractor to that.
Promotions seem to normally equate to more responsibility with a meagre if at all pay increase for permanent members of staff. People forget that there is only 1 CTO in an organisation, not everyone can ever get to that level. Most get stuck in middle management hell doing unfulfilling jobs.