Well, it's strong? I'm sure if you used one right, it'd be a powerhouse in its own right, but I figure flexibility gives you more options to work with. Fire never struck me as a defensive type, anyway.

[After all, fire burns, but it's easily doused. Even Flare, for all his strength, is more of a speedy attacker than a tank.]

As for why they're not around, well, they're rare. I've only ever seen them out on Cinnabar, and given how many people barely make it past Goldenrod, it's easy to see why they're in short supply.