Why does the EP500 Split Phase output cable have two L14-30P inputs?

I recently ordered a split-phase cable for my AC300’s although I somehow ordered the split phase for the EP300 by mistake:

When I looked at this cable it didn’t make sense to me. The input ends are L14-30, and they join to an output L14-30C. Is this not already two split-phase outputs joining to a split-phase output? Why would you need 4 hots joined to make a single output with 2 hots?

The interfaces are different and not compatible, you need to proceed with a return and exchange.
The fusion box of EP500/P is P020A, while AC300/500 is P030A, they are different.

This does not answer my question.