https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3528014/

>Hypothesis 2: Spontaneous Decidualization evolved for embryo selection
>
>A more recent idea, with experimental support, argues that SD evolved to allow the mother to sense embryo quality upon implantation. Teklenburg et al. [24] used a human co-culture model to study the interaction between decidualizing ESCs and blastocysts and found that ESCs trigger a strong response against impaired embryos but only upon differentiation into decidual cells. These authors argue that SD evolved to compensate for the high rate of chromosomal abnormalities in human embryos, allowing the mother to limit her investment in bad embryos. In support of this hypothesis, the same group showed that women with impaired decidualization responses are not able to sense embryo quality, evidenced by increased fecundity but also recurrent pregnancy failure [25].

It's not the only reason, but it is likely one of the reasons behind why humans menstruate so frequently. It's a waste of resources so there would ostensibly need to be some sort of evolutionary pressure that makes it a valid expenditure. Prioritizing your best embryos and discarding less than ideal ones minimizes nutrient loss rather than find out later after a significant time and resource investment that you've got a nonviable pregnancy.