The reason, OP, is that games didn't get patched in the old days except on PC (and even then, for a choice few set of games).
If a game was broken at launch, it stayed broken. And Nintendo wouldn't allow that. They had to do extensive bug testing first instead of shipping first and then patching later. Were there still bugs? Absolutely, but they were rarely immediately obvious for well-made games, unlike, say, Bethesda games today.
This is especially true for game-breaking glitches.
If a game was broken at launch, it stayed broken. And Nintendo wouldn't allow that. They had to do extensive bug testing first instead of shipping first and then patching later. Were there still bugs? Absolutely, but they were rarely immediately obvious for well-made games, unlike, say, Bethesda games today.
This is especially true for game-breaking glitches.