In the manga, Krillin doesn't stop training. His sense of duty and the need to protect his comrades push him to keep improving his skills and strength.
It's hard to say exactly. It could be that the manga wasn't meeting the expectations of the publisher in terms of quality or market demand. Another possibility is that there were legal or rights-related complications that led to its discontinuation.
One way to stop reading manga is to set limits for yourself. For example, only allow yourself to read for a certain amount of time each day and gradually reduce that time. Also, try to focus on your goals and remind yourself that too much manga reading might be taking away from achieving them.
The HxH manga stopped possibly due to the author's health issues or creative burnout. Sometimes creators need a break or face unforeseen circumstances that prevent them from continuing.
The Berserk manga could have stopped because of a combination of factors. Maybe there were legal issues, or the author decided to move on to other projects. Also, it's possible that the fan response wasn't as expected, influencing the decision to halt the series.