Also styling has to change every 3 years, so that everyone can tell, that you're poor/tasteless/uncool, if your car doesn't look like the latest styling fad. If they can
Since sportiness is a major design driver these days, and coupés used to be sporty, you can make your sedan sporty by making it look like a coupé. Then middle aged men with disposable incomes can buy that coupé without their wife telling them, that they need a proper car. Makes for better economics of scale, if you can sell the same pressed sheet metal to small families, travelling accountants and mid-life crisis afflicted gentlemen. Which is probably also why SUVs are working so well.
Make a sporty looking sedan and a butch looking SUV, and you have 90% of the car market covered.