Hallo Theodore,

why do you think, default of ports is '1'? Would it be possible to have default '0'.
Of course, it would, but current limiting circuitry of assumed active pull-down would violate TTL compatibility. There is much more deviation from +5V rail allowed than from 0V rail in TTL norm. And so, it's advantegous to implement current limiting circuitry in an active pull-up, than in an active pull-down.

Bye,
Kai