Unlike Lice and Fleas
Bedbugs actually for the most part don't hang around after feeding, but move back into "hiding". This is why it is so hard to get rid of the buggers. And while a truly nasty infestation will have them filling a mattress, they can also be found in cracks, behind walls, and so forth.
A good washing will dislodge vermin, and send them down the drain (maybe alive, but they are still out of one's linen), bunging items into the dryer for a good roasting removes/kills even more.
However think about it, from one's bed one travels all over the home, and the vermin travel with you, hopping or getting dropped off as one makes one's way to the toilet or kitchen each morning.
