If Del Piero went on a whole season without scoring a single goal and was Juve's worst player, most members here would still be pissed off at a manager benching Del Piero, so i wouldn't read too much into that.
Maybe Del Piero had a falling out with Ranieri, but lets not be revisionists here, almost everyone at the time thought Ranieri wasn't good enough for Juventus and most wanted him out, now after seeing how low Juve has sunk with other coaches, people are changing their minds about Ranieri and wishing he stayed and looking for other reasons(and other scapegoats) other than his ineptness. Which most probably was the reason Ranieri was sacked.
There was almost a consensus that Ranieri wasn't good enough for Juve at the time, in hindsight, maybe that wasn't true, but fact of the matter was, Ranieri was heavily criticized by fans at the time, and most wanted him out. Maybe the board had similar thoughts.