That’s because they outsourced all their dirty manufacturing to China, which has since picked up the pace of emissions. No country exists in a vacuum - the global economy we all participate in is financing the climate crisis.
Which is also why any climate agreements that don't include the third world are pretty much useless. They'll just drive the energy-intensive stuff out of the country, harming their economy for little actual improvement. Kyoto etc are just kicking the can, pretending to do something to shut up the rabble.