Why does the Host in the Prologue to The Canterbury Tales suggest a prize for the pilgrims at the end if they win the challenge?

I assume that the host does that because he wants the best
chance of having a bunch of really good stories.

The way I
see it, the host was going to be hanging out with these people for quite a long time on
the way to Canterbury for the pilgrimage and on the way back.  Imagine how boring that
would have been back in the days of now portable DVD players or iPods or
anything.

So the host wants to be entertained.  I think he
figures that he'll get better stories and be more entertained if he offers a
prize.