I’m going to dispute this. It’s a regional style. My cite: I learned how to make pasta in Italy from an Italian restaurant owner.
In the south, the lasagne are assembled including layers of ricotta. In the north, it’s made with layers of a cheese sauce — very similar to a French Mornay, béchamel + Parmigiano. It’s not just béchamel. Also, the lasagne tend to be thinner and more delicate.
They are structurally similar, in terms of pasta + sauce + cheese, but the mouthfeel is entirely different. The cheesy sauce is the correct choice for what the northern style of the dish is going for; the heavy ricotta is the correct choice for what the southern style is going for.