Why can't Attack on Titan games use the title on Europe?

In Europe copyright issues have forced Atlus to change the action game's title.

Atlus didn’t release any details or hints about who issued a copyright claim against them for Attack on Titan but the official European Union trademark database (OHIM/CTM) contains details of the copyright filing and the subsequent opposition for Attack on Titan (CTM013347331).

PT Entertainment Limited issued the complain because of their game Titanbet and winner:

Timeline of events:

10 Oct 2014 – Trademark application by Kondansha Ltd for “Attack on Titan” wordmark under classes 9 and 28 (covering computer games and electronic games)

25 Nov 2014 – Application published for opposition with a deadline of 25 Feb 2015 for any trademark opposition to be filed.

25 Feb 2015 – Opposition filed by PT Entertainment Limited against “Attack on Titan” under grounds of “Likelihood of confusion”.

26 Feb 2015 – OHIM begins investigations into the validity of the opposition claim and informs Kodansha Ltd about it.

6 March 2015 – OHIM declares the opposition claim is admissible as it is based on an earlier right for “Titan”.

11 May 2015 – Expiry of ‘cooling-off’ period

12 May 2015 – Beginning of adversarial part of opposition proceedings

11 July 2015 – Deadline for submission of further material to substantiate earlier rights.