I have some conjectures as to why that may be:
1. High variability of pay, not only between companies but within companies. As a SWE your total compensation can be expected to double every two promotions, and promotions can be pretty fast. Promotions are also not purely a function of tenure like other professions with steep comp growth such as pilots.
2. "This is too good to be true" syndrome. You show up at your comfy 250k job with catered lunch, dinner, and maxed out benefits. After the first month, your workload is about 3-4 hours a day. Everything is flexible - the time you show up, the time you leave, the days you choose to come in to the office, what you wear. Everyone is smart and nice. Free snacks. Imposter syndrome and paranoia set in. Am I doing enough? Should I look at this P2 prod bug on a Satuday? I guess I only worked 20 hours last week so it's fair to work a couple of hours on the weekend. Everything I do needs to be perfect or they could've just hired someone in India for 1/10th my pay, right? etc. Then it snowballs. (I'm probably just describing imposter syndrome.)
In reality nothing really happens if you slow down and do things at a comfortable pace. Most managers want to cultivate reliable people who take long-term deep ownership, not productivity machines that just bang out features. If they needed more output, they'd just hire one more person.