After birth - why pads and not tampons?

Becca • Baby #2 due in January, baby #1 one year old
Might be a stupid question, but why do we need to get pads for the after birth bleeding instead of tampons? Is it because there is too much blood for a tampon to absorb or is it because you shouldn't be sticking anything "up there" so soon after the trauma of giving birth? 
I'm stocked up on overnight pads, they look as thick as the newborn diapers lol, just wondering why we can't use the more comfortable tampons.  Thanks!