Why don't nonrigid airships have multiple gas cells?
With the loss of one cell you also lose the same fraction of lift. Unless you can drop an equal amount of ballast quickly, having some more gas cells isn't much of an advantage – the ship still falls out of the sky.

The Zeppelins could lift up to three times their empty weight simply because they became more efficient by growing larger. Blimps are small, so their lifting capacity is restricted. Carrying so much ballast would require a much bigger blimp.