The thing is, there are millions of routes for you to explore from
For example, Australia has several major as well as regional airports. If you see full route in Sydney and Melbourne, try operate international flights from Perth, Adelaide, etc.
Why squeeze for that pie of Sydney-Los Angeles when you know eventually you will lose money?
Not worth it at all in my opinion
Another clear example, if you are operating Los Angeles-Shanghai Pudong and that route is oversaturated, then you can consider opening Los Angeles-Shanghai Hongqiao. But some spammers, already have big profit LAX-PVG, still comes in for LAX-SHA when he clearly sees that LAX-SHA is already filled up.
LAX-SHA has 300 seats as of 2007, go grab that if it is empty.