Many people couldn't travel because the fees of transportation were too high for them.
Whether it was the giant birds or the horse-drawn carriages, not all families could afford it, and in addition these means of transportation usually took a lot of time, which discouraged those who could afford it from using them.
For example, using a giant bird from Dawn city to go to the capital city would take 2 weeks, and using a carriage would take more than a month.
So, if nothing was done to facilitate the transportation of people, humans and demons would never meet.
And in order for their cities to prosper, and grow, they needed people who could open businesses and receive a lot more costumers.
