Why did Emirates order so many A380s?
Given that most of us don't sit in airline boardrooms it's difficult to say for sure why an airline favors one particular aircraft over another. But I'll have a go anyway. The A380 was initially marketed as having unbeatable costs per passenger compared to similar aircraft, i.e. the 747, so if you wanted to carry a lot of people a long way it was a logical choice. 

In reality, those unbeatable costs only come if you can actually fill the seats. The introduction of the A380 coincided with rising fuel costs and the Global Financial Crisis. Less passengers and more expensive fuel helped the business case for heavy twins such as the 777, 787 and now the A350, and most airlines have preferred those types to the A380.

Emirates love the A380 because of some fairly unique circumstances:


Emirates operates a hub and spoke model in an excellent geographic location. It has its main base in Dubai and most of its business comes from connecting passengers through this one city - i.e. passengers travelling between Asia, Africa, Australia and Europe.
Emirates carried 58 million passengers in FY2017-18. How do you carry this many people through one airport, without running out of space? The answer is in bigger aircraft (and soon a second, bigger airport). Other airlines with such passenger numbers usually have multiple bases, and more point-to-point operations.
Finally, Emirates is less sensitive to extra operating expenses than other airlines due to its low cost base. This is largely thanks to favorable government conditions (such as labor and tax laws). Some even argue that they receive outright subsidies from their government.