Adopting anything as blind dogma is Expert Beginner territory. See also: DB table normalization.
Those 2 years were to do the data migration and of course there were different priorities, if that would be priority we would do it in 1 month, but we liked to spread risk over time.
Reason was of course performance issues and not really needed joins, where normalization didn't bring any benefit.
If you ever find a job in an ideal world, hold on for dear life and please accept my CV for consideration.
Pragmatic approach: generally end up with an average of around 2.72 normalization across all tables.