Can’t speak for the OP but it’s often about what’s most valuable at different points in life. Depending on where you are in the US, having kids can be a formidable experience. Poor leave, expensive childcare, etc etc. It can change the calculation for whether the extra money in the US is actually worth it.

Right out of school it was fun and easy to drop everything and go somewhere cool (SF, NY, etc.). Can tell everyone you work for a flashy big tech company, make a ton of money, and have no responsibilities.

But eventually life catches up to you, especially if you have strong family/social roots in Canada. It's not easy to bootstrap that in a new country.

I was also there under a TN Visa and had a few border experiences that rubbed me the wrong way since the TN Visa is a bit hand wavy and up to the border guard at your time of entry. The hostility at times from the border guards didn't make it feel like I was returning "home". Sure, I worked for a company that had an army of lawyers to fix it if anything went wrong but it still leaves you with a sour taste. I can't imagine they're getting any friendlier these days.

Lastly, I didn't mean it like 5 is some magic number - some stay less, some stay more.

It's a myth that US income tax is always lower than in Canada.

I worked in the US for a bit when I started out. I paid more income tax in CT than in Toronto on the same salary.

I just wanted to come back home. Even in small town CT, there were areas we were told to stay away from after dark.