Why do international wire transfers cost so much and require so much time to complete?

It costs money to move money. There are so many people, systems, networks and processes involved, all this costs money. Besides this is a for-profit process, so money is made by each individual entity.

Why it takes long? Depends on from where the wire was originated, the cut-off timings for processing transactions, the time difference, that agreed time frames to keep float on the money, etc.

Two answers will shed further light on your question:

• Faisal Khan's answer to Why does it cost money to wire money?
  
• Faisal Khan's answer to What exactly happens when a wire transfer is made? How does the money travel from the sender's account to the recipient's account? How much time does each step take? What regulatory measures are in place, if any?