Not trying to be a smarta77 or anything. Honestly would like to know why a separate rod is required for a square bill as opposed to a regular crankbait.
That's kind of my thought too.
"Required" is too strong of a word. The reasons I have a dedicated SB rod are:
1. I like always having one tied on and don't want to take off deep diving crankbait to switch to a SB
2. For deep divers a long cast is key. For SB's an accurate cast is more important. Long casts use long rods, accurate casts short(er) rods.
3. I use 12 lb fluoro for deep cranking, or smaller. I use 17lb abrazx for SB's.
You can do both on the same rod but you can do it better on a dedicated setup.