Why did the brother do what he did in the end?

Wasn't just a change of Heart. It was wanting his Life to have some good... Some positive meaning.

I wrote the following in another post:

"What also strikes me as odd is the evident consensus that Salim pulled a massive flip-flop at the end of the film, changing from pure evil to doing the right thing. Were you all paying attention to what went before? I don't think it was such a sudden change. Throughout the film he was very pragmatic, but he also always looked out for Jamal and saved his hide several times. He saved Jamal from the Fagin-like creep (forget his name, but he collected orphans whom he used as beggars) who was planning to blind him. Why didn't he just sell him out then and get in good with the creeps. He did it a second time after their return to Mumbai - Jamal went to find Latika and they were caught by that creep. Salim saw (perhaps correctly) that the only realistic option to save them was to kill that creep and go to work for his rival (bringing Latika as tribute). They were portrayed as having two entirely different characters: Jamal was extremely idealistic and stubborn, so that it took Jamal's realism and willingness to act (even doing horrible things) to keep them alive. So it could be argued that he chose the path of violence and evil to save his brother, then chose death to save his brother. It is worth pointing out that in all cases, he could have thrown Jamal under the bus and got in good with the bad guys. He never did that. I'm not arguing in favor of joining a mob and killing people (which evidently was his job), but I think the story should be seen in its fuller nuance, with all of the dilemmas presented. Part of the point was that the slums of Mumbai presented challenges to survival that the pragmatic Salim was adept at navigating, but that may have destroyed Jamal had not his brother been their to protect him.

In the end Salim concluded that Jamal was simply not going to give up in his quest to be with Latika (that is what he told Latika when he helped her escape), and he knew that would end badly with Jamal being killed. So he sacrificed himself to save his brother (and Latika). It was nothing new, as he had done it before in the film."

Because he had no IT skills and couldn't get a job at Microsoft