Why Lord Buddha didn't stay alive till the end of this "Kalpa"

I have heard that __Lord Buddha__ once told __Ananda thero__ that a Buddha can live till the end of a __Kalpa__, if he wishes so. He did this because he wanted Ananda thero to invite him to live till the end of the Kalpa. But, Ananda thero did not invite him as __Maaraya__ was inside his head. My question is, if Lord Buddha was able to read minds and see future, why did he asked that question in the first place ? Why didn't he lived till the end of this Kalpa himself ? What I am missing here ?