A series connection is an all or nothing circuit, as each igniter is daisy-chained to the next, dependent on one another. If one igniter fails, the whole circuit will fail. Consider a strand of Christmas lights; if one bulb is missing or burns out, the entire strand is defective unless the faulty bulb is replaced. A defective igniter will cause the same issue in a series circuit.
Advantages of series wiring: Being able to fire more igniters than in parallel, and if an igniter is defective, it is quickly identified as continuity will not be displayed due to a broken circuit.
Disadvantages of series wiring: Individual defective igniters could prevent all igniters from firing, depending on the defect.