Advanced Engineering Tech - Curious about firing order

I was on a long drive today and started thinking about how header primary length and diamater affected the powerband. I was all set out to do the math only to find that i knew nothing about firing order.

What i don't understand is why the designers did not arrange firing order to the banks were constantly alternating. Can anyone help me understand the reasoning behind this?

To fire in an alternating bank sequence, the crankshaft would have to be 180° (flat)... there are engines like this, and my understanding is that they have balance and/or harmonic problems.

The OEM's have discovered that a 90° (crossed) crank balances easier, but the firing order does not alternate banks.