While I rarely actually ever check a bag, it is still nice that WN allows free bags.
What I would be curious is what % of people flying WN actually bring 2 checked bags. 2 checked bags seems excessive to me especially considering that there network is all domestic or near international destinations. I don't think the % would be very high so the added revenue would be minuscule but I don't think there would be any public backlash for charging for the 2nd bag if the 1st is free.