Being HN, you have to be careful of selection bias. I'm sure many of us know someone who left a 150k/yr job in Vancouver, say, for 400k in the valley. Or may be that someone.
But to suggest this is th norm for software jobs across both countries? The stats just don't support it.
3-4x is crazy. You make it sound like the US is crawling with tech jobs paying > 500k for mid-career jobs. It just not so.