Or increased, as the case may be.
A bot just does what it is told. It cannot 'think' on its own, so it has no ability to adapt to circumstances.
Due to the minimal AI that D2 uses for its monsters, it's usually not a big deal that it cannot adapt, as the monsters behave pretty much the same every time. There is, however, the rare occasion that a monster can act a little differently, and do something unanticipated that could result in a character death.
If you were invulnerable during bot runs, either A.) Blizzard supports botting or B.) There would be no point to dueling, as everyone would be exploiting whatever bug made bot users invulnerable.
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