Specifically English Protestantism, in this case. Some things were allowed to be polyphonic, such as Psalm settings, and Byrd made a point of setting Psalms that alluded to the struggles faced by Catholics at that time. Some referenced the desecration of Jerusalem, others were the known last words of martyrs.
Sicut Cervus (a setting of Psalm 42) is such an example.
This is stated a bit too broadly. Some protestants preferred that, others didn't. Bach didn't have a problem with polyphony, for example.