What's the difference between a trophy species and a non-trophy species?

I often wonder about this topic as who can really say they have the authority to call a trophy a trophy and who cant?
Why should Rowland Ward or SCI decide that certain species are good enough to "make" the book and others not?
I suppose if it has horns,antlers or tusks there seems to be consensus they "make" the book because they can be measured.But what about the cats?They don't have horns,antlers or tusks yet they're in the book.
What about the impressive Zebra? They're not in the "book" although they have a skull like the cats.
Why should some be left out while others enjoy all the glory?

I'm sure the folks who put the record books spent a lot of time discussing this issue: is size really always the goal?
At the end of the day it is each individual hunter who decides what is HIS trophy and how much hew rates it.
The bushpig probably doesn't look as regal as the sable antelope to most but that's just looks..what about all the other qualities like degree of difficulty that are attributed to species?Surely they count too?
Fortunately these other qualities are mostly in the eye of the beholder as they can't be measured with a tape.

I'm happy to say the bushpig makes the "book" as a trophy species in both publications and is much more than that in my eyes too.