I’ve noticed over the years that 99% of western bits only come in a 5” width, whereas English bits have sizes ranging on average from 4.5 to 6.5”. I never gave it too much thought before but now I’m curious if others pay attention to bit size or not really. 

I do pay attention to the mouth piece size, I have a 14.1 mare and a 15.2 mare and some in between so they have different widths on their mouth.  If you order your bits from a bit maker you can have them made however you want.  Carolina Bit, L&W Bit, and Shallow Creek Bit all make good bits that are affordible.