The reasoning is totally the same as why people buy real designer bags or designer anything, from each respective side (some people can't comprehend why people even buy designer anything)
1. They appreciate the design
2. They can (or cannot) afford it
3. It makes them happy and nobody can tell them otherwise
4. It's their money
The trafficking and labor conditions for fakes are sad, but hardly exclusive to the fake industry. It creates a lot of jobs in developing world, not just the manufacturing side but buying and selling.
Drugs are bad. But people who love designer bags aren't going to be deterred if their favorite designer is a cocaine addict. The person who buys fakes also undeterred by drug trafficking.
I'm not in support replica fake stuff, but I've seen how obsessed people in Asia get about designers, I think both the real and fake has its own market that is driven by the same concept actually. The concept of class, elitism and luxury life.
That's just..... sad.....