Well, in the same way that all Android or Apple smartphones have the same core software package - doesn't stop individual variants having bugs.
They are cars not computers. The hardware is significantly more complex and more prone to failure in ways a software patch won't fix.
I would argue that a car with fewer than one hundred thousand moving parts is less complex than many pieces if software out there. I can't say whether they are more or less prone to failure, but they can be fixable.
Of course these things are fixable but not with an over the air software update. Getting your car fixed, especially if it takes a day or more is a problem I wouldn't want to deal with.