Well, one reason why that might be for me is that a lot of my summer stuff is minimally lined. Some jackets (aside from lining over the canvas) have only lining at the shoulder, going just half way up the shoulder line to the neck, so that at the neck and upper back, there is no lining at all...and and some of these do not have the sleeves lined either. The fresco and linen are naked and free.
Given how little lining there is in the first place, the marginal differences between ermazine and Bemberg do not prove significant in practice in my set of applications.