Is this necessary or just a habit? On few occasions, I heard that carbs are the focus before a workout and any protein is fine (chicken etc).
Just a personal habit. I don't like to eat heavily before working out, especially since I usually workout somewhere around 9-14 o' clock.
But there is science behind it. The reason I take fast whey protein 30-60minutes before a workout is because whey protein causes the highest spike in amino acid levels around 60-90 minute mark after digestion. Casein has almost twice as slow benefits, which makes it better for post workout. Mixing whey with milk has the benefits since milk is both whey and casein.
Meat is also quite fastly absorbing when it comes to food. So it's not a bad idea either. I'd recommend eating a meal 2-4 hours before a workout or so.
And yeah, carbs are important depending of goals. There are arguments on why carbs might not always be the best thing pre-workout, but it works for me and supports my goals.