So I did a search, I was curious. The results were almost all speakers are larger than 4.5 inches, as you found out, except for one 4 inch clarion speaker. My theory is that more folks want a decent sound so the larger speakers will give more "oomph" so to speak.
I installed three flush mounted Fusion speakers that I'm quite happy with and decent sound. My suggestion go to a larger speaker, you only live once....lol.