Because they have a problem with storing the worlds plastic and turning it into a usable material/product at the end of the recycling.
It also probably costs a lot more then before and global emissions of CO2 and other gasses created that they no longer wanted.
Plus, recycling doesn't save much energy, Shipping it on huge ships is extremely damaging to the environment. Ships use a special type of fuel, it's the worst and most polluting gunk that nothing else can use, creates the most pollution.
Glass is one of the most efficient products to recycle, but only saves around 5% energy then just creating new glass. The only reason (currently) to recycle, is to manage waste, not save energy or emissions.
They just got fed up with being the worlds dumping ground.
If you think about it, it's a HUGE plus for the environment, air and everyone. Countries now have to deal with it themselves, so will either create more recycling plants or import less waste packaging/plastics.