So why does evolution does not explain everything, and especially culture

Here is summarized the conclusions drawn by Felipe Fernàndez-Armesto in his book "A Foot in the River":

Basic to entente biology and history is the acknowledgement of three facts: that culture is not uniquely human; that the existence of culture depends on evolution in the sense that we can only do anything with the physical and cerebral equipment evolution has given us; but that culture also changes independently of evolution, which should not be expected to have infinitely elastic powers of explanation.

(Chapter 8, "Towards the planet of apes") Felipe Fernàndez-Armesto goes on:

The mutations that make for a multiplicity of culture are different from those that kick off organic changes: they are capricious, but not random; they are devised by minds, not spontaneous; typically, they do not replicate according to the incidence of any advantage, nor does their success or failure respond necessarily to environmental constraints or opportunities.

(Chapter 8, "Towards the planet of apes")

See this old blog post that is relevant to this topic.