Samsungs flagship is the galaxy series and that's the overwhelming majority of their smartphone sales. Its not like sales are spread out evenly among all their models.
People are just not as excited about Samsung as apple. There's no need to try to explain it away further.
Indeed, they make 1 flagship model that SOME buyers wish to own.
They also make a wide variety of other phones, all with different features, in different sizes at different price points to appeal to other customers and release them at other times of the year.
So this does not happen, like it would not happen if Apple did the same.