Well, why won't Game Freak make Charmander die when rain gets summoned? Why won't Game Freak make Sudowoodo flee from battle when Water type attacks and rain get used on it?
Answer: It's most likely impractical, and it's just the Pokedex entry.
Most of the time, things from Pokedex entries aren't true in the games, and Arbok isn't all that special. At least Arbok has some significance to the silly Spinda. Like the Charmander and Sudowoodo example, the Arbok thing fits with that, and Pokedex entries don't have to be true in the games.
Anyways, that's my theory. I hope this helped clear things up a bit.