How does Finasteride cause ED when it does?

The NHS wrote: This US study looked at a medical records database to see how common erectile dysfunction (impotence) was among men prescribed two drugs, dutasteride and finasteride, both used to treat non-cancerous prostate enlargement. The drugs work by blocking the male hormone testosterone. A low dose of finasteride is also used to treat male pattern baldness. Overall they found that around 1...

Source