Your mind becomes better at whatever repeatedly captures it.

Whatever regularly takes your attention is what your mind gets practised at. Hours of fragmented scanning make you good at fragmented scanning; hours of sustained thought make you good at sustained thought. The capacity is shaped by use, in both directions.

Look honestly at what has captured most of your attention over the last month and consider what that has trained. If you want a different capacity, you have to give it repeated hours. The mind follows what it is repeatedly given.