Poker games take time (hours), people grow tired, computers don't.
This is a good point. Computers have no emotion, either. Even the best human players are affected to some small degree by their emotions, especially when they are tired.
People struggle at memorizing chances, taking shortcuts, computers have exact picture talking into account every single bit.
Not much of an issue in Hold 'em. Good players can handle those odds with little effort.
All one needs is behavior that is random enough, for human players not to guess if computer is bluffing.
You of course don't want the human to be able to guess when the computer is bluffing, but it's certainly not "all one needs." Not by a long shot.
Then, of course, there is luck factor, so results will fluctuate quite a bit.
Yes. They'll be playing 1500 hands per day, but in no limit hold 'em the outcome often comes down to a handful of key hands.