The practical reason is it's not clear how long they would survive. These embryos are in a petri dish, unless they were to implant them in a women's uterus I'm not sure how long they would be able to develop.
You might be able to develop them longer than five days, but then you hit the ethical issues. The entire moral argument for abortions is based on bodily autonomy of women, and that those rights trump the rights of an unborn fetus. But for raising a fetus in an artificial environment there is no body autonomy argument.
Another issue is murkier, and is based on the circumstances. Generally abortions are used by women who did not intend to get pregnant as a last resort form of birth control. When you're performing abortions for scientific purposes it's different, and there are different ethical standards to consider.
You might be able to develop them longer than five days, but then you hit the ethical issues. The entire moral argument for abortions is based on bodily autonomy of women, and that those rights trump the rights of an unborn fetus. But for raising a fetus in an artificial environment there is no body autonomy argument.
Another issue is murkier, and is based on the circumstances. Generally abortions are used by women who did not intend to get pregnant as a last resort form of birth control. When you're performing abortions for scientific purposes it's different, and there are different ethical standards to consider.