Translation of ”in fact”

I suspect it’s because "en fait" isn’t always a good translation of "in fact". According to Lawless French:

While both (en effet and en fait) can be translated by "in fact," there’s a difference: en effet serves to confirm or agree with something that was just said, while en fait marks an opposition or contradiction.  (Ref: https://www.lawlessfrench.com/expressions/en-effet/)  

In the sentence you quote, "In fact" introduces a confirmation of or enlargement on the previous sentence, there is no opposition.