Hit record, money flowing like water, follow up record money still flowing, buy houses, cars, trips, houses for friends and relatives, maintenance and insurance on houses and cars, staff for houses, travelling chefs and then there are the managers who need to be watched over constantly or they dip into your money.
Then one day the new album isn't selling so hot and the one following it isn't so good either, but you still have all these bills that need paid and people depending on you, record label asking for recoupment money and that is when the fast decline begins. Happens faster with some than others but if you live like a baller in this game it will eventually catch up to you.