The Ruthless Reality of Amazon's One-Day Shipping
gizmodo.com
gizmodo.com
This will always happen. As something becomes more popular, the supply of drivers increases, the demand decreases, and it becomes more difficult to make money as easily. This is natural to any market.
In 1998, you could make over 6-figures if you knew simple HTML and could throw a website together. Because there was a rush of people learning HTML, you now need to have a much bigger skill set to make that wage.
Driving is not that difficult. Anyone with a license and a good record can do it, which qualifies the majority of adults in the US. I wouldn't expect this job to pay that much.