Tamerlan Tsarnaev wanted to get righteous. He wanted to cleanse his soul and his life of anything that might displease Allah or run counter to Islam. And so his piano playing, as accomplished as it apparently was, had to go.
In which scenario would the world be a better place: one in which Tamerlan Tsarnaev became or remained essentially a Muslim in name only, maintaining an indifference to his faith’s teachings of hatred and violence against unbelievers, and becoming a pianist of some accomplishment, or one in which he rejected all that was sinful and dedicated his life to Islam, such that he eventually got the idea that murdering some infidels at the Boston Marathon would be a capital way to please the god who commanded him to “slay the idolaters wherever you find them” (Qur’an 9:5) and to “strike terror into the hearts of the enemies of Allah and your enemies” (Qur’an 8:60)?
It was, after all, the same commitment to the teachings of Islam that led Tsarnaev to give up music on the one hand and pursue jihad terror on the other.