It’s wholly illogical to claim that Nowitzki “took an 80% pay cut”. The team turned down a $25 million team option, but that’s not the valid point of comparison for Nowitzki’s new contract. The valid comparison is “what would Nowitzki get as a 39 year old free agent coming off a season where he missed 1/3 of the games due to injury and was a fairly mediocre player when he did play?” Last season, he was 28th among power forwards in ESPN real plus minus, and slightly above average per player efficiency rating but slightly below average per box plus minus and win shares per 48 minutes at Basketball Reference. I don’t know for sure exactly what he’d be offered as a free agent, but it’s far less than $25 million per year.
As for the Amir Johnson comparison, Baumann simply ignores that, setting aside name recognition and past achievements, 30 year old Amir Johnson is, right now, quite likely simply a better NBA player than 39 year old Dirk Nowitzki.
So, Nowitzki definitely isn’t taking anything like an 80% pay cut. Perhaps he is taking some pay cut compared to his free agent value, but that becomes a fairly easy to understand trade-off. Rather than Baumann’s financial question based on a faulty premise, how about this one: why would Nowitzki leave playing in the city that he reportedly makes his home — with his wife and three young children—in order to add a low single digit percentage to his already substantial career earnings and likely net worth?