Presumably all that material went through an editing process of some kind. Readers don't know what errors were fixed before publication, but we can see the ones that weren't.
Fixing mistakes -- and doing all the other useful things that editors do, such as checking context and tone -- is time-consuming and expensive.
For example, the German magazine Der Spiegel (The Mirror) employs 80 fact-checkers, according to the Columbia Journalism Review.
But some facts are more equal than others, or at least they used to be.
A long comment attached to the CJR article by sociologist and journalist Hersch Fischler highlights the historic role of Der Spiegel fact checkers in digging up dirt on the magazine's political enemies.