The problem is that they have a largely demolished economy. They have absolutely monstrous natural resources but have suffered constant depredations from Russia and had only recently began to improve. The EU won't accept them because Ukraine cannot meet the entry demands at all because of how weak the economy is and they would instantly be the largest recipient of EU equalization payments, to the point of constituting a massive drain to the collective funds. Furthermore, the Ukrainians are massively conservative in comparison to the Western Europeans, are heavily religious and are generally very independance minded. They would make natural allies with Hungary and Poland and would further cement the position of the eastern bloc which stands in opposition to EU federalism and the reduction of member-state sovereignty. Germany, France, Belgium and their client states will NEVER allow the Ukrainians into the EU. Instead, ukraine will be granted "candidate status" as a means of pressuring them and extracting political gains, like what happened with Turkey, before their candidacy is ultimately rejected.