When I started my first job as a DBA seven years ago, my project was to migrate several SQL Servers and all the servers were in SQL Server 2000. In my first SQL class at my school, I started my learning with SQL Server 2012. It was a shock to me to work on SQL 2000 databases at the time (as I am not familiar with the SQL Server 2000 yet), especially as it was my first job as a DBA.
My first project was to migrate approximately two hundred and fifty SQL 2000 SQL Servers to SQL Server 2012/2016. It took us a couple of years to successfully migrate all these Servers.
Deepthi mentions fear as a demotivating factor. In fairness, fear is a valid response to upgrades for two separate reasons: first, because the changes they release might break your existing code (something very common in the data science world); and second, because new code has new bugs that you haven’t discovered or worked around yet.