It isn't true that elliptical (or early-type) galaxies are metal-poor. This sounds like a pop-sci myth being propagated. The first line of the abstract of [Pipino & Matteucci (2006)][1] states that "Elliptical galaxies probably host the most metal rich stellar populations in the Universe". Thus your suspicion of the idea that "ellipticals are metal-poor" is well-founded. Measurements of galaxy metallicities and metallicity gradients have been around for decades and show that ellipticals obey fairly simple scaling relationships between mass, luminosity, velocity dispersion and metallicity - the so-called "Fundamental Plane". In terms of metallicity, massive ellipticals with bigger velocity dispersions are a bit more metal-rich than the Sun, whilst smaller galaxies may get down half the solar metallicity. The range is *much* larger for spiral galaxies. In addition, there is a tendency for ellipticals that are *older* to have higher metallicities. Examples of these trends can be seen in [Graves & Faber (2010)][2] and [Li et al. (2018)][3]. *The central plot here (taken from Graves & Faber 2010) shows how the metallicity of galaxies varies with their stellar velocity dispersion (an indicator of their mass). [Z/H] is a logarithmic base 10 scale where 0.0 means the metallicity of the Sun and -1 would a tenth the metallicity of the Sun. You can see that the elliptical galaxies (red) have a relatively narrow range of metallicities, that most are as metal-rich as the Sun, that less massive ellipticals have lower metallicity and that spirals (blue) have a much bigger range of metallicity.* [![The fundamental plane from Graves & Faber (2010)][4]][4] The reasons behind these trends are still debated. But as you rightly point out, ellipticals likely form from mergers of objects that have already been actively forming stars. A low metallicity is therefore not necessarily expected. [1]: https://arxiv.org/abs/astro-ph/0610831 [2]: https://arxiv.org/abs/1005.0014 [3]: https://arxiv.org/abs/1802.01819 [4]: https://i.sstatic.net/RWXX6.png