Apologies to be blunt, but I believe the answer falls something along the lines of: "None of your business".
When it's your money, you can wonder about what to do with it. If it's not yours, then what the owner is or isn't doing with it is of no concern to you.
Lol, I think you have dealt with people like franky so much that you forget to snap out of your defensive mode. What if OP is just a curious teenager wondering and trying to learn?
@OP, the answer is : because they are gold hoarding dragons, and they love the sound of coins when they dive into the pools of coins.😉
Bitcoin addresses are like transparent vaults, everybody can see them, if all the bank accounts in the world were the same, you could see the same for millions of people not touching their money, gold etc.