Originally Posted by Grumpy McTrumpy

you only have so much traction available, and once the radial forces push it beyond its breaking limit then there goes your wheel.

guess where those forces come from? mass+velocity (enginerds will say acceleration I guess)

it is better to spread that force between two contact patches.

your evidence that most normal riding is unevenly on the back wheel is in your tire wear, so any movement to the front is not going to unweight the rear, but make the bike closer to evenly distributed.