My theory is that noone wants to be in a place that makes them feel uncomfortable. I mean, if you did something completely against your moral compass, would you actually want to be in church the next morning? If you rob a bank, do you want to listen to a monologue about the 10 commandments? If you went out & got irresponsibly drunk, then chose to drive, & pulled a hit & run, would you want to go face your beloved grandmother & explain why you did it?
The same thing applies to Heaven. Since God knows everything we have ever done, wrong or right, would you want to be in his presence, knowing that you have let him down?
Besides which, most Christians believe that sinners will be sent to Hell, from which there would be no way to get to Heaven.