One of the responses I see most commonly for one of the (many) reasons mothers return to work to be WOHMs or WAHMs is feeling fulfilled by their jobs. What is it about your job that gives you fulfillment? Do you work in a profession where you're helping people (teaching, nursing, non-profit, etc), are you fulfilled by accomplishing goals, do you like the feedback you get from your boss?

I personally am not fulfilled by my job and am not in the position to be able to find a new job right now. I continue to do it because it pays well, but it's certainly not something I would be looking forward to going back to after maternity leave.