Why was the report unpublished to the public for two years? The reason is simple: The study found no link between illegal downloads and a reduction in legitimate purchases of digital goods across several categories. In fact, the study found that sales of games specifically increased in the face of piracy. The takeaway with that little factoid is that developers putting microtransactions into their games has led pirates to actually buy the games they download illegally.
The study was done by Ecorys (and many kudos to them for running a clean study even when clear it flew in the face of what the EC expected to see) and it surveyed users in Germany, UK, Spain, France, Poland, and Sweden looking at four types of digital content. Those content types include music, books, audio-visual materials, and games. The report found that an average of 51% of adults and 72% of minors have pirated digital content in those countries.
The highest rates of piracy were found in Poland and Spain. The study looked at displacement rates, or the impact that piracy has on legitimate sales. The displacement rate for music, books, and games were found to be negligible or even non-existent. The rates for film and TV were in line with previous studies on the topic, but it's not clear what those previous rates were. Presumably there is an impact from piracy in TV and movies, but that is unclear.
The final takeaway of the report is that there is no robust statistical evidence that piracy costs content makers sales. The real concern for many here is that the EC sat on the results for two years because the study didn't fit the narrative it wanted to draw of piracy being a menace and costing companies money, and thereby workers' jobs. In fact, the only reason we even know about this study now is because of an official request by a member of the EU called Julia Reda.