Morning menu in Hamburger shop

There are some franchises of a hamburger shop in Japan, such as McDonald's, Lotteria, Burger King, and so on.

Actually, I do not like these shops so much. Nonetheless, I sometimes utilize them for some reasons, waiting for a person, spending time, and taking a breakfast.

Most of them offer different menu from regular ones in the morning. For example, you cannot eat a hamburger at McDonald's in the morning. Instead, muffins and pancakes are available exclusively in the morning.

I was wondering why McDonald's provides these meals. In the US, muffins and bagels are very popular as a breakfast. However, I guess few Japanese are familiar with them. Process to cook is quite different between hamburgers and muffins. It may be efficacious for a shop to provide the same menu in whole the day.

I read some articles via the internet to know the reason. As a result, there are several hypotheses that McDonald's offers specific meals in the morning.

(1) Variety of food
McDonald's offers different meals in the morning, so that customers who have come in the morning will come to McDonald's again in the afternoon.
The writer of this comment insisted that there is an evidence to prove this hypothesis. However, I myself dare not to go to the same franchise twice in a day.

(2) Transportation
McDonald's offers meals only not using vegetable in the morning, because fresh vegetable is difficult to transport from the farm to each shop in the morning.
This opinion is denied by another commentator. Actually, some shops sell meals with salad in the morning. It maybe depends on the location.

(3) History
The other day, McDonald's began to sell morning menu, leading to a great success. Therefore, this custom is long lasting till now.
I think this reason is too weak to explain today's trend among hamburger franchises.

There are some other reasons claimed. French fried potato is required to be cooked at once with a large amount. Instead, hashed potato is cooked separately. So hashed potato is advantageous to provide in the morning when a few customers come together.

At least it is certain that it is impossible to offer both regular menu and morning menu at the same time. You have to choose the food you want to eat in accordance with the time you go to McDonald's.