The government, more specifically the Federal Reserve, wants to convert to all plastic or some other form of "secure" currency.
They want this so that they can monitor and control you and your money and to get rid of the underground economy, which is around $800 Billion in the US today, some estimates are higher.
Likewise they want to stay away from any form of currency that is based on any real value, like gold, because they want to control the value of your dollars.
They are trying to chip away at currencies any way they can. They spend billions t try to convince you that plastic is better for you and they are trying to go back to using coins, because they are impractical for us.
But all of these things are aimed at the ultimate elimination of real money because they want to be able to charge a fee on every penny you spend, and they want to know exactly what you spend, where and with whom.
If they own your money they own you and that gives them ultimate control over your life for their benefit.