Unsuccessful in Torah Study - Leave yeshiva for parnossa?

Igros Moshe (IV #36.14) Question Is it permitted  for unsuccessful students to leave yeshiva to study other subjects. You write that there are many yeshiva students who are afraid of sin and therefore they are not involved in the needs of daily life and they sit in yeshiva with an open sefer but they don’t actually learn anything and thus there learning is not successful. Answer It can’t be that they make such an error but their real motivation is that they are simply lazy. Even if they were actually learning according to their abilities but they were not going into depth but merely skimming the material this is being lazy and is considered serious bitul Torah . They need to be chastised and explained the error of their ways. If they don’t accept this from their peers they need to hear it from the rosh hayeshiva.