Because fruits and vegetables lose a lot of vitamins and antioxidants after juicing, even more than cooking. Even after squeezing the juice, drink it immediately.
This is because the cells of fruits and vegetables have complex ultrastructure. Just like a unit, there will be many rooms, and each room has its own duties. Things are different and cannot be mixed together. For example, vitamin C must not meet with various oxidases, otherwise it will interact. However, when juicing, the rotating blade destroys all the cells and all the cells are mixed together. In this way, vitamin C will naturally suffer heavy losses when it encounters a variety of oxidases. The result of oxidation can also be seen from the change of color.
So, if you can eat whole vegetables and fruits, you should make your teeth work and squeeze them into juice and pulp in your mouth.
Now there is a concept that juicing is particularly healthy, which is actually a misunderstanding. Juicing is a measure to promote the intake of fresh vegetables and fruits when they are inedible. Freshly squeezed juice itself has not brought about the improvement of nutritional value, even if it is not done well, there is obvious nutritional loss.