“Lilmod, besides expressing regret one must change his ways. If Dr. Ephraim Shach regretted the way he turned out why didn’t he go to learn in Ponevich and take over his father’s position?”
As DY put it: “If it were only so simple…”
Same reason we don’t do a complete turn-around every year (even though we sincerely want to, and perhaps even take steps in that direction). Maybe he did try to do what he could at that point in his life, but at that point in his life, he was no more capable of taking over his father’s position than I am (well maybe a bit more than me).