If our attention doesn't get regular exercise it withers and becomes weak. You actually have to practice and exercise the attention for it to become strong, it doesn't happen on it's own and it won't happen if you continue to do the opposite of what is require to be attentive, that is, always in a state of distraction.
Practicing being attentive does take effort, unlike many of the other activities that present themselves in life as we know it today.
I personally find that reading a book that was written at least 100 years ago helps train the attention, any artistic type hobby like painting or sculpting or etc etc.
It really is a case of use it or lose it.