Most of japanese home don't have an oven included in a kitchen stove as we european and american know it.
The average japanese kitchen usually have a cooktop with a fish grill included like this ( yeah, grilled fish is a serious matter )
so, an eletric oven ( like the one she used for the pie or for the pizza with sausage and pinapple) is a nice extra for cooking but they totally can live without if they eat traditional japanese meal ( i.e., mostly rice, soup, and fish....and fried food because hey, let's eat something tasty and greasy like fried chicken once in a while)
and lastly, convection oven microwave combo are a thing.
@Kaarme Where would you put it? Japanese household kitchen is really small, the same goes to other Asian countries. Our cooking styles don't require oven, most dishes are fried,simmered, boiled, steamed or grilled so a small oven for occasional baking sweets like this is enough. As an Asian, I had never seen or even known what an oven is for 19 years, and I lived in the biggest modern city in my country. The first time I saw it was when I moved to the US and even now my family don't use it, the oven had became a place to store breads and dry foods.
@miyako19
It's not a household, though, it's a dormitory. It seems pointless to have equipment not capable of serving the whole place. But of course this is manga, so a 2 liters pan can make enough soup for 20 people.
Even though this is a big kitchen serving a lot of food, it's been constructed traditionally. So it probably was never built with a full sized oven in mind.