Your brain learns to do what you teach it. As indicated above, if you practice concentration, your concentration will get better.
I fell out of reading books for many years, now I'm back on the bandwagon. I've been cranking on books for about six months now. Once I got back into the rhythm, which took about a week, I was able to settle down and really read again.
Concentration is a choice, just like multitasking. All the cool kids showed off by doing many things at once, and now we think that's normal, but it's just a fashion like any other fashion. I've noticed a rise is "put your phone away on holidays," for instance, or willfully putting your phone down in meetings. This is an acknowledgement that multitasking doesn't work in many situations.
You may also need sleep.