And here is a quick example of how this can happen.
Cowboys resign their DE for 3 years. Contract is for $50MM with a $20MM signing bonus with a base salary of $10MM each year. Cowboys keep the DE all three years, having spent the $50MM in cash.
The Eagles resign their starting DE for 3 years. Offer him the same contract. But they cut him after 2 years. They paid him $40MM in cash over the 2 years. They sign a new starting DE in Year 3 for 3 years, $60MM with a $25MM signing bonus with base salaries of $5M in Year 1, $15MM in Yr 2 and $15MM in Yr 3.
After three years, the Eagles would have spent in terms of actual cash on their starting DE $70MM ($40MM spent on DE #1 in 2 years, $30MM cash spent on DE #2 in Year 3).
The fact the Cowboys often hold onto players too long and don't use FA is a big reason why they are low in cash spent. Now you can call that smart if you want but the reality is the Cowboys literally are near the bottom of the league in terms of actual cash spent on their roster over the periods discussed in that BtB article.