I think no-hitters are overrated in general. They're kind of neat, like when a batter hits for the cycle, but ignoring walks makes them less meaningful. Nobody would call a game where a pitcher has a 3 hit, no walk shutout a "no walker" and nobody tracks how many 0-walk complete games occurred in history.
Ryan had allowed 2 baserunners, the perfect game was not in play and he wasn't going to get to pitch 2 more innings. It's a team sport, why not let someone else try to finish the no-hitter.