He's fitting in. He's a spy. If he wears tactical gear all the time he'd stick out like a sore thumb.
Look at the James Bond films, and when Bond gets into fights. He's either in public being chased or chasing someone, he's being ambushed in a room (or a train car, or an elevator, or a stairway) or he's been caught and trying to escape. When he is going into a situation where he is not caught unprepared he usually dresses appropriately (see For Your Eyes Only, Live and Let Die, On Her Majesties Secret Service, etc.)
One more thing – It's also a sign of the times and the people Bond associates with. Back in the 1960s and 70s men wore suits all the time. Additionally, Bond investigates people that are usually in the upper echelon of society and, well, he has to dress well to associate with such people.