exists.

My guess is that typically when a word has a vowel-consanant-e, the vowel is typically a long-sound for that vowel:

Ride, pope, dope, dire, etc. (Though as I make this list, I realize there are plenty of exceptions to that.) So if I didn't know the word and was trying to read "Frige," I might sound it out "fryge."

Thus, my guess is that early English writers threw the "d" in so that we'd know not to make the "o" a long "o" sound. Another one is the difference between Lodge and Loge. Bridge, Judge, badge, etc. If you take out the d. . .Brige, Juge, Bage, then pronunciation gets a bit more confusing.