Pirkei Avos: Work Isn't Necessarily Bitul Torah, Bitul Torah Is
The Mishna says in Pirkei Avos (4:12), "Limit your business activity and learn Torah... If you are Mivatel Torah you have many bitulim against it." Shouldn't it say if you do not limit your work you have many bitulim? Another question is why do you have "many" bitulim against it?
Rav Chaim Brisker said that when they ask you in Shamayim if you learned a great deal of Torah you will be justified in answering that you didn't have time because you needed to work long hours to support your family. However if during your free time you didn't learn and wasted your precious opportunities with Havlei Olam Hazeh, you will not only be held accountable for the time you wasted but also the time you spent working to support your family. Why? Because you now have proven that even had you not been working you would not have learned since you had no misgivings about squandering the perfect opportunity. Now the fact that you work will not be an acceptable excuse for you lack of learning.
So from this one instance of Bitul Torah suddenly you have opened up a can of worms and let out many more charges against you for things which you originally were protected against and you now need to explain all the Bitulim.