The main difference between the two forms of green tea is the process by which they are made.
While green tea takes the leaves of the plant and makes them into convenient tea bags you can brew, green tea extract is taken from the leaves and efforts are made to keep all of the nutritional value.
Both offer a similar amount of nutritional value, and the main benefit of taking green tea extract over drinking a hot cup of green tea is that it’s far more convenient to ensure you get the benefits in your system every day.