2 years seems too short. IMO you start looking less valuable at some point because anyone looking to hire you knows you're going to bail in 2 years, which may reduce their willingness to invest.
[1] https://www.independent.co.uk/life-style/millennials-jobs-ca...
Staying at a job for a while is a means, not an ends, and as such not necessarily something to optimize for.
Myself having 0 felonies makes me below average (as 8% of Americans have at least 1 felony), and I don't see myself striving to be above average in this category ;)
[1] https://globalnews.ca/news/3946085/switching-jobs-pay-boost/
Both my mother and her father worked at the same place (a General Electric appliance factory) for most of their lives. My grandfather was there on day one and remained until he retired. My mother started there ~20 years after he did and was there until the day they shut down. I know of one man who worked there for 44 years!
Switching jobs every two years seems so foreign -- and somewhat "suspicious" -- to me.
The last year? I think the rot set in during the Thatcher/Reagan era. Corporations showed they had no loyalty to their employees so they shouldn't be surprised when their employees respond accordingly.