Soldato
Because opportunities don't fall from the sky for most people. Their side projects suddenly don't become twice as lucrative as their main job, and their job doesn't put them on a path to acquire skills that are worth 2x in the market. You'd have to be incredibly fortunate for this to happen to you.
Nonsense. I changed jobs 4 years ago, and while I haven't quite doubled my earnings in those 4 years, I'm over 50% higher than where I was before, in a job I enjoy more which is closer to home, however to get here, I worked my **** off for a couple of years prior to develop my VB.NET & C# skills in my "spare" time (what little there was trying to also juggle working full time and a young child), and then applied for an internal junior position which involved being seconded to a customer's site 40 miles/~1.5hrs away (compared to the 15 mins on the bike to the company's office). It then took me several weeks of applying, and 4-5 interviews before I got the current position (which initially involved a pay cut during my probation period).
Tell me again about those opportunities falling from the sky?
Surely if most people aks themselves the question "can I earn more money" the answer must be yes - it's more a question of commitment to it surely?
Absolutely. There's nothing stopping anyone learning a new skill in their spare time or doing a distance learning course to learn new skills and gain qualifications.