It's also a Big Mac because of the way it's cooked on the grill, the way it's seasoned, and the way the burger is put together. Have you ever worked at McDonald's?
The meat that goes on the grill in McDonald's is cooked in 30 seconds or less. I forget the exact time, been years - but I distinctly remember that I put 9 frozen pieces of really-cheap (seriously, they had documents pinned to walls and easily ready by employees - what they buy for their food is so ridiculously cheap and in such ridiculous bulk, that I'm shocked it's not being air-dropped for starving people in Africa) all-beef patties on the grill, shaking some salt/pepper over each one, then pushing the button on the grill. A big secondary heating plate comes down on top of the meat, pressing down against it, and it all stays like that for a good thirty seconds (or however long the exact time is supposed to be). Then, after it's cooked, I pile all 9 of those burger patties into a heating tray, that's left sitting at the end of the sandwich-making line for... I think it was up to 30 minutes, for somebody to order a product that uses that particular bit of meat.
On top of that, the grills aren't regularly cleaned properly between batches. You basically scrape it, put more meat down, and go again. Soon you've got a nice thick coating of burger grease being cooked alongside each beef patty.
I guarantee you, Olive Garden does it different. (do they even serve burgers? If they did, I doubt they buy the same bulk-boxes of frozen beef patties)