Honest question since I'm not familiar with the area - who is making 400k at Microsoft or Facebook? Not the typical mid-level software engineer, I'd assume. Are these product leads or head engineers making the 400k?
I work hard when I'm at work, and really focus. I don't do a lot of the extra-curricular stuff that you can easily spend your time on. I'm an L6 and last year earned just north $450K with decent performance reviews. I have damn near a million dollars in unvested $FB RSUs, too, so there's almost no chance I'm going to leave for anywhere that won't match that with equally liquid public shares.
¯\_(ツ)_/¯
For Google, it looks like 90% of L6 engineers and a single-digit percentage of L5 engineers are at this number. So yes, not your typical mid-level engineer (many/most engineers plateau at L5).