As stated by Don, and confirmed by Lippert, the parallel path is the path of "least resistance." By hooking the two breakers in parallel allows the current to divide equally (since the breakers have equal resistance) across each breaker and combine as a sum to the device. Yes, they could have easily increased the capacity of the one breaker, but that is not in their supply chain and it is just easier to send a duplicate breaker and add it in parallel. Lippert admits that the current being drawn by the motor is a litle higher at times than the breaker can handle.
I guess Lippert never figured there would be dirty cogs and other abnormal behavior of their motor that would cause the current to go higher than their rated breaker.