I think the animal names, styles, are part of the culture like the old Chinese "legends" and storys. Not really meant to be believed as such. Maybe they match up human characteristics with some animal they like or has historical significance and they go with it.

Think about it...there are many "pure" dragon styles but I cant begin to tell you how the last dragon I saw may fight.

Pure tiger....such a huge beast with masive claws and teeth.....Not sure if a human could pull off a pure tiger style.

Crane....well that is a stretch for you.

Snake, well, without venom and only being able to wrap around the opponent...Im not sure that would be such a great "pure" style.

Praying Mantis, chewing someones head off is an option but....

Monkey would be the closest thing to what a human would do. But, other than their strenth I havnt seen them do many refined techniques on each other.

You have a very valid question.

I think people have been making systems up for thousands of years and it continues today. It would be hard to have "pure" anything.

Maybe it just sounds a little cooler for them to say I teach "TIGER" style than I teach "Leroy Jenkins" style.

Not meant to be a negative post at all and as I said before it is a legit question.