Magic cards also have resale value, where Warhammer shit generally does not. A well rotated trading collection stays valuable, and the staples that go in decks for non-rotating formats (modern, legacy, vintage) rise in value significantly faster than the rate of inflation, making them an investment, so long as you manage your collection by buying and selling at the right time.
That said, it's a hobby that requires as much attention as your stock portfolio. When done right, the cost is your time, not your money.