What makes egg whites and almonds a good combination
There is nothing special about the combination, you seem to have stumbled over a case of confirmation bias :)

Here I made a table with examples. The table is by no means complete, it contains the first things that came up in my head. As you see, all other combinations of whole eggs or egg yolks work with almonds, other nuts, or no nuts at all. If the combination you noted were somehow special, I wouldn't have been able to find examples for other, not-working categories.
So, combining almonds and meringue is the perfect combination for a macaron, and combining almonds, egg whites and flour is the perfect combination for a financier, but only because that's what makes a macaron a macaron and a financier a financier. You can use any combination out of {egg whites, eggs, egg yolks} and {almonds, other nuts} and each of them tastes good and has been used for something in the kitchen.