Well we are in it too.
Corruption and human rights violations have been our hobby for hundreds of years.
It’s easier to bring about change with them inside the tent I think.
Make membership conditional on the changes, and the benefits become something real that they would then worry about losing.
Membership was conditional to changes. They hadn't been met hence ukraine wasn't a member. Now they are offering membership without having to meet those conditions.
Other countries such as bulgaria had to raise their standards to get membership and they did. Which was good for the bulgarian people. The eu also then invested in the country to improve it economically (poland and ireland are great examples of this).