It's really not a problem for places with decent public transportation. There are parts of the world where it makes sense to have a monthly or annual pass. I've no idea what it is like in the area where this occurred though.
The Skytrain in Vancouver goes from the downtown to YVR in about 30 minutes. It is possible to go to the airport and back on a $2.75 ticket (on weekends and holidays; the ticket is valid for 90 minutes).
I don't specifically know about Xi'an, but I remember in 2012 subways in Beijing were a flat 2 rmb (about 0.35 USD) and in Shanghai something like 2 to 4 rmb depending on distance. Nanjing was similar, but I don't remember the specifics. So assuming all Chinese cities that have subways charge the same order of magnitude, this loophole would have indeed been valuable.
