There some less-ethically challenging reasons, explained well in their nature paper, namely that using controlled environment they learn a ton of things about h

There some less-ethically challenging reasons, explained well in their nature paper, namely that using controlled environment they learn a ton of things about how embryos grow > The ability to remove a mammalian embryo from the uterine environment and grow it normally in controlled conditions constitutes a powerful tool to characterize the effect of different perturbations on development during the period from gastrulation to organogenesis, that can be combined with genetic modification, chemical screens, tissue manipulation and microscopy methods