Fizzy drinks are fizzy because they have lots of a gas in them called carbon dioxide.
On Earth, when you drink that drink, all of those fizzy bubbles rise to the top of the drink in your stomach and cause you to burp.
And you’ll notice that if you have ever drunk a fizzy drink, they cause you to burp quite considerably!
Trouble is in space there is no gravity to cause all those gas bubbles to rise to the top of your stomach so you won’t burp and all of that carbon dioxide will stay inside you.
That causes a lot of problems if you swallow all of that and it goes into your digestive system so for that reason they don’t have fizzy drinks in space.