Why do you think the rich and powerful people get monuments and status erected in their money?

I think that you mean "in their memory". I'm not sure which sonnet you are referring to. In any case, in a general sense, rich and powerful people might like to leave some sort of visual legacy of themselves. I suppose they might feel that a statue validates their importance in history. You can't take anything with you, after you are dead, so you might want to leave a permanent reminder to people of everything you had.