You are correct. Greggs's main draw is "it's there".
They are everywhere, they are cheap, they are betting than eating cardboard and they appeal to that sense of Being British that works well on so many people of this small island. And so, they sell plenty of not great sausage rolls.
I remember after trying the vegan sausage roll when it came out thinking: it's not disgusting, but I can't tell where the pastry ends and where the sausage starts.