Pilot training up to the level required for even the most basic job (instructor) is going to cost $50,000 or more. You can't pay that back on a $20,000 a year salary. Pilots do it because they love flying.
Disclaimer: I am a private pilot doing my commercial flight test in ~14 hours time.
This situation is completely correct. I've lived on sweet fuck all incoming for 5 years (think less than $25000AUD). My training here in Australia has totalled to around $110,000AUD - not including interest on loans etc. After my test, I'll have ~250 hours total flight time. If I manage to get a job straight after my test, in reality, I can probably earn $35-40k AUD. How do most pilots in my situation survive? They get a second job. Not only does this add to fatigue, it certainly doesn't make things safer.
Why do I do it? Because its friggin awesome. If you want to fly to make a buck, then you live in another world.
In a nutshell, the aviation industry is fucked. Everyone wants to cut their costs as far as possible without violating the law. This means cheap labour in maintenance, cheaper pilots, crappy pay and benefits.
I really miss the wages I was paid in network administration, they were double what I'll get here....