These cars can be found all over the place. In my building there is an 850csi covered in dust(not sure what year) and an M6, amongst others. They are very common in Dubai. I drive past a fairly new Audi A4 on my way to work that has been parked there for about a year. Abandoned cars are very common in Dubai but dont think that it just some rich guy that left it because he was bored with it. As the previous answers mentioned, these cars were owned by people that found themselves in debt and had to leave the country or was confiscated because the amount of fines exceeded the value of of the car.
You can find tons of amazing cars at the police impound. Most of them even have their keys inside. Literally hundreds of cars. I found quite a few rare and classic cars as well. At least a hundred bikes too.
I have taken these pics on an excursion to the impound. Very sad to see. Cars not in the pics that broke my heart was a dark blue s65(~2012) with collapsed air suspension, paint was peeling and all rubber cracked. It must have been parked there for 2 or 3 years, so I guess mileage must have been low. There was a Bentley Continental with only one rear window open, and about two years of dust and rain entered this tiny window, back seat and surrounding area was trashed, rest of interior was ok though. There was a yellow 911 convertible with its roof down and the interior was no longer recognizable. Seats were completely destroyed.
In the pics, the saddest car is probably the F430 spyder, parked with windows down but ready for a restoration. The RS5 just arrived and hardly had any dust on it, but will probably be there for a long time.
As for the last part of your question, buying these cars are not impossible, but incredibly difficult. Cars have to have all cases against the owners dismissed, all debt dismissed or paid off, and then if the owner does not claim them back, the cars will go into police auction. There is a long queue of car restorers and car flippers waiting to pick these cars up for a bargain.
Edit: This answer is getting slightly popular so I thought I'd upload a few more pics.
Edit: Lots of people are asking about the size of the impound. I took this pic from Google Maps so you guys can see the size of it. There is a much larger impound right next to it, and there are quite a few of these impounds in Dubai and in the UAE. Thousands of cars going to waste.
Edit: Sorry for the edits, but just to respond to people saying that this is a waste, please realise that all countries have car impounds, and with this being Dubai, a few exotics is not completely unexpected. All these cars have court cases pending against them, and they cannot be sold without all necessary protocols being taken place and all fines been either paid or written off. These cars were most likely owned by people that lived above their means trying to live the Dubai life, but not everybody owns an oil well. We call this “the illusion of inclusion”, or more simply, “King for a day, fool for a lifetime”.
Edit 28/05: Went to the airport last night. Found these gems parked there. Behind me were another three. Mini and Golf V GTI also parked in background. I should have taken one home. Can't imagine what the parking fees would be. I was there for 15 mins and they charged me 30AED(~10USD)
Final Edit 13/08/2018:
Hi guys! Thanks again for the overwhelming response from the Quora Community. Just to let you guys know, I went to the impound last week, and it has been completely demolished. All the cars have been removed, all walls knocked down, and nobody that was present could tell me what happened to the cars. They wouldn’t let me take photos at all, so nothing to post.
There are still tons of abandoned cars on the streets and behind warehouses all over Dubai. I am planning on starting a database of these cars. I have found a Hyundai Centennial, 2014(with a few years of dust on it) and a Maserati 3200 GT (with the boomerang lights) just parked in the middle of nowhere.