Wow, you are a super strong asset to your family! They are lucky to have you looking out for their best interests.
The younger brother has probably not faced enough real consequences in life to realize how bad things can get.
In his defense, he probably feels like he wants to enjoy a more peaceful life, and not feel stressed about working all the time, or facing repeated failure. Often times, I find I need to be by myself doing things that calm me down before I can tackle any hard work or face a difficult decision. Social problems sometimes sort themselves out with time after all.
How often do you find yourself solving problems for him? Maybe he knows you will do things for him when he withdraws, or he thinks his attempts are pointless.
This can spiral into a lifetime problem of bad habits and flawed decisions, unless he learns early on that he can be happy, successful, and encouraged when he puts a positive attitude into chipping away at his goals. Young people often have not learned how to control or change their emotions, and can often feel a slave to their negative self thoughts. It is good to get them to open up, so they do not hold it in until it becomes depression. Always remind them why they are loved, no matter what they may think, say, or do.
Who am I to give advice? Wishing your family the best. Remember you are blessed.