Because they have been so absent from European politicsin the past 200 years...

From EUobserver.com:

EU to hold atheist and freemason summit

Brussels is to hold an EU summit with atheists and freemasons in the autumn, inviting them to a political dialogue parallel to the annual summit the bloc holds with Europe's religious leaders.

While the EU is a secular body, the three European presidents, of the commission, parliament and EU Council, alongside two commissioners, on Monday met with 24 bishops, chief rabbis, and muftis as well as leaders from the Hindu and Sikh communities. The annual dialogue, which has taken place since 2005, is for the first time this year made legally obligatory under Article 17 of the Lisbon Treaty.

Under pressure from Belgium, which constitutionally protects and financially supports humanist organisations as well as churches, the EU has been forced to hold a mirror-image summit, but of atheists, scheduled for 15 October.

However, in a move that perplexed and annoyed humanist groups, the EU atheist summit will also welcome under the rubric of ‘non-religious groups', the Freemasons, the secretive fraternal organisation, according to commission spokeswoman Katharina von Schnurbein.