Why is it hard to concentrate on Kusala?

When I try to concentrate when studying, I end up with a wandering mind, but when I'm watching a video, I forget all the other things. Why is it hard to focus on things I really need? Is it some kind of practise? This was a lot easier to do for Lord Buddha, Ven. Arahant Moggollana. Is focusing on Akusala than Kusala in samsara the problem? Do I have to build up practise of focusing to overcome this?