I think you miss the problem structuralism is trying to solve.

As Robert Pirsig said; " Science works with chunks and bits and pieces of things with the continuity presumed, and the (artist) works only with the continuities of things with the chunks and bits and pieces presumed." Structuralism created models of the world as a set of relationships that fixed the problem of science being atomistic. Certainly, this is what drew Piaget to structuralism.

Poststructuralism believes in a set of relationships, but not a fixed 'structure'. In the Postmodern phase poststructuralists thought all structures are socially constructed. I think Postmodernism killed structuralism. You can't be gender fluid if you believe there is an underlying structure governing sex.

To say structuralism was short lived is patently false. Ken Wilbur is clearly a structuralist. Many of the people labeled as 'poststructuralist' were in fact structuralists. As you point out Foucault was a misunderstood structuralist. I also think many of the French Marxists owned more to structuralism than to Marxism. Lefebvre for example.