The problem is that you have to treat religion equally and for a lot of European countries that would mean pushing Christian symbols out of public offices as well. Most Nordic countries, Greece and Malta have crosses on their flags for example. Many countries like Germany have parties, which are explicitly Christian. The Bundeswehr uses the Iron Cross as a symbol, which is in direct heritage from a crusader order.
The problem for those countries is that baning Islamic symbols is very often just racist rethoric to hit Islam, rather then a proper separation of state and religion.