The thing is, you need to take into account the fact that a lot of the political "deals" are not done during official EU sittings, when these translation services are available.

A lot of the discussions happen during the informal after-hours in cafes and restaurants.

This is one of the reasons why, for many years, the Dutch delegation was very unsuccessful at pushing their own interests and placing their representatives in "important" positions, as they were all keen on taking the first train home from Brussels, and were skipping these informal gatherings.

It's not a stretch to imagine that a poor mastering of the "important" EU languages will put a politician at a disadvantage in such settings, due to an inability to communicate with his/her peers.