UPS had around 80% of the US small package market in 97.
So, simply put, UPS delivered around 8 or if every 10 small packages.
Today, UPS delivers around 2 or 3 of every 10 small packages delivered. The current market leader is USPS, they got into the market heavy as email and online banking bill pay, etc decimated their first class mail bread and butter.
UPS' share has dwindled from 8 in 10 to around 3 in 10. Because, as the overall market has exploded due to online commerce, UPS was not competitive enough in largely price, to grab as much of that business as the competition has.