EU expansion has always been since about exploiting the cheap-available labor present within those countries, First was the southern european countries which had pro-western dictatorships and crushed any forms of self-development in favour of money being siphoned into a few elite, and the east had the collapse of socialism and the wave of neo-liberalism which created rampant drug epidemic, unemployment in the millions, and the loss of the welfare states, these factors made people desperate for 'western salvation', and created sufficient anti-communist propaganda like the EU being the only bloc which had uplifted these nations, and thus deserves praise.

With the EU expanding into these countries those desperate enough to feed themselves will take any opportunity despite how awful, or humiliating a job can be. Often leaving their country to permanently move to western ones to even experience a crumb of wealth that the western middle class experiences, the expansions also destroyed a lot of the labor movements present within western countries and the ones targeted by expansion. Causing inequality to swell even inside the wealthy nations in the EU.

The other one is political. The expansion of the EU into your nation completely locks your country politics into serving western neo-liberalism, violent even fascist politics become the norm, as the image of EU prosperity fails to even materialize in these countries, the stage to address the failures of EU-finance capital will inevitably invite fascist elements into your nation. Take for example baltic nations, poland, and romania, where the choice to vote is either fascist parties, or conservative capitalists.

To summarise here, the expansion of the EU isn't necessarily a bad thing in itself, but that the actions which lead up to that expansion is inherently scummy. The use of NGOs, financial capitalists, and carpet baggers to dismantle the local economy forces you to accept this expansion, otherwise you're country is at risk being completely exploited without the petty crumbs thrown at your way by western saviours. Otherwise you'll end up as ukraine, a country so broken and corrupted is rather used by western elites as a weapon rather than a slave. So either you're given a choice to receive bread crumbs, or be used as a weapon.