There is a like a billion economical reasons why shouldn’t governments do that but the simplest reason would be that there would be a whole lot more cash in the market and the more cash there are in the World means the less it will worth.
Say you have 1 apple and you are hungry and someone came in and said he will give you 10 dollars for your apple, you would refuse it because you are hungry and you need it but if you have 1000 apples and hungry and someone says he would pay 10 dollars per apple you would sell like 990 of them.
Meaning the more cash there is , the less worthy it will have.
This is only part of the picture. If I issue a few trillion dollars in some private accounts (as people do), perhaps printing up a few billion in cash and storing them in my garage (as people do) this will NOT immediately affect the trade down the street at the grocery store in any way. The people buying apples don't have keys to my garage, and the store owner also doesn't have the keys. So, the price of apples STAYS THE SAME - despite that massive cash injection. In fact it will take decades for enough of this cash to start circulating to affect prices.
Because people claiming to be your government have shown they don't care very much about future prices, imagining that having cash in their garages is more important, they will continue to issue massive bank accounts and fill their garages with cash. Business as usual, well not really usual but the last fifty years or so at least.