It's a confluence of multiple factors including Turkey didn't want to carry low performers in the Euro while it was booming, plus a lack of willingness to harmonize with European practices, laws, and standards. Maybe 5-10% of it was racism, but not necessarily a major factor.
Turkey's GDP per capita is a lot lower than that of the EU. A lot of the EU accession talks stalled around human rights and recognition of Cyprus which was an existing EU member. Of course Austria did not want them in - but unless fundamental changes were made with respect to the two things above accession talks would have stalled regardless.
Turkey sits right at the access point between EU and all the Central Asian countries with a lot of oil. This made Turkey an "attractive" nation for the EU economically. Socially though they just are not there.
Here’s the timeline: Turkey got stamped as an EU candidate at the Helsinki summit in December 1999, while the southern Cyprus didn’t hop into the Union until May 2004.
That five-year gap tells you Cyprus couldn’t have been the first roadblock for Turkey’s talks; the island only became an issue once it was already inside the club.
When Turkey finally sat down for formal accession talks in October 2005, the Cyprus dispute had wrapped itself around every single chapter, turning a one-on-one quarrel into a full-blown EU-level veto.
