why do BMW go down in price so soon ?

Because the timing on it wares down alot faster than the other cars in fact the best out of ten on a BMW performance is much lower than what people think those cars are no good they don't last

All cars depreciate in value.

interesting answers, guys- the real reason the BMWs depreciate so steeply is that they are so expensive initially- one might say "overpriced" and everyone knows that they require special maintenance- and if that maintenance is neglected, the second owner would be looking at very expensive repairs- nice cars, great to drive, but you need a separate bank account to take care of the beast- the repair costs are subtracted from a second buyer's offer to purchase- this is why you should keep every single maintenance and repair record when you own a BMW- or a Mercedes for that matter-

BMW likes to price their cars pretty high from the factory, but any car will depreciate very rapidly. My mom bought a 2013 Elantra new, which was around $20,000 at the time. As of now, the car is worth around $10,500. I've worn myself out on this site saying this, but I'll do it again... BMWs are not expensive to maintain compared to all other cars on the road. All cars need proper maintenance, it's just that some are stupidly reliable and any idiot could run it on zero maintenance for 150,000 miles. The difference is that these higher end cars use higher end engines that can't take the abuse of people who don't know or care. And it gets expensive for some because they run to the dealer for everything... and BMW dealers are known for overcharging on maintenance. They aren't going to be as cheap and easy to deal with as your Honda dealer, for example. Sorry, rant over.

And they do last... my 528i has over 170,000 miles on it and runs like new. Maintenance is key.