AFAIK EU is pushing to fix this through Eurozone and tax harmonisation but some European countries don't feel like it. Probably they have an advantageous position or an industry they would like to protect.

Like the whole idea behind EU is basically fixing this. It started as a single market and through the years Europe is trying to bring the continent together and how stuff should be done(all the EU standardizations are essentially about ironing out the legal differences between ~30 countries so that it function like one single country). Not there yet, unfortunately.