Long term employment is very important to increasing productivity as a software engineer. The first 6 months is just learning existing systems, so from 6 months to 12 months doubling productivity is normal.
As you work longer you build more infrastructure that supports future productivity gains so from 12 months to 24 months you should be able to double your productivity again.
After 24 months your productivity is so much higher than newer employees that you can continually invest time in developing tools and infrastructure to enhance your productivity so your productivity continues to grow.
When there is a recession there will be unemployment for software engineers so a certain percentage will not be able to find work.
These job hoppers are the lowest skilled since they have never learned how to develop their productivity over the long term and they will be demanding the highest salaries based on their past experience so they are the least likely to be employed.
This situation is only happening because of bubble cash and a lot of inexperienced leadership with too much money on their hands.
Once the bubble pops you will see all of these people with a resumes full of 6-12 month stints and outrageous salary expectations working at Starbucks (if they are lucky) and everyone who puts in years for reasonable salaries still employed at profitable companies.
Enjoy it while it lasts.