It could be out of boredom, stealing to get a thrill and the adrenaline rush. He might need some stimulation an exciting hobby perhaps, climbing, parkour, diving etc.
Could be due to peer pressure to be in with the "cool kids", then he need a talking to of what is really cool like saying no, maybe a bit of self esteem there as well.
As some above says it could be that he wants to be seen, to be noticed and loved (not saying you don't love him just that it might not be obvious to a kid). Spend more time with him, involve him in what you are doing more.
Might be none of them or could be a combination of all of them.
Maybe get him to due some regular volunteering with people really having it bad, homeless, victims of burglary etc to open his eyes a bit.
Also I don't completely agree with the "Always gets what he wants and does not want for anything." this could be part of the problem. Not knowing the value of things as he never had to fight for or save money to get things. Make him do chores for things, save up money if he wants a lot of things and maybe give him a carrot like a goal to look forward to if he behaves and doesn't steal.
Whatever you choose to do I hope it goes well for you.