The main reason is water loss, and then there are other reasons, just like the chaff in the heart of a tree after a long time ... pickles will taste bad after a long time. There may also be microbial decomposition.

Pickled vegetables are best preserved on the same day, and the content of harmful substances such as nitrite will increase from the next day, reach the highest value on the fourth day, and then gradually decrease, so pickled vegetables are best preserved on the same day, or after 20 days.