Why does my sourdough loaf not get an ear
with no photo of the crumb it's hard to know whether there's also a proofing issue but irrespectively let me tell you that it's notoriously difficult to get a consistent ear at home unless you bake the bread in some sort of hot enclosure (dutch oven, cast iron pot with lid etc). That is my experience at least. Sure, the cutting makes a difference so as to have a nice ear but the moisture is the main culprit: your oven cooks the outside of the bread too fast before the temperatures reaches the air in the inside, so when the bread expands air is sealed in and doesn't get the spring it can. Cooking in an enclosure keeps the moisture from the bread close to the crust thus keeping it soft for a bit longer which is when the inside gets hot and expands. This whole thing happens the first 5-10' of baking so if you don't get an ear by then, it's game over.
I have been baking sourdough 2ice a week for about three years now, here's a bread that didn't quite open well enough (together with its crumb to show that it's properly proofed and folded)

and here's one that opened beautifully:

their only difference being that the second was baked inside an enamel pot (the baguettes always get an ear cause they are baked on their little baguette baking trays).