Flu comes in cycles some years deadlier than others. The 2 or 3 before covid were mild strains so, in the developed countris atleast, we had a fair few vunerable people living on borrowed time. That's why nursing homes were hit noticably. You could say the same for people with underlying conditions. In the third world I expect flu is not such a big thing and there are other non seasonal issues that take out the old and vunerable.