Raw is not a finished product like JPEG tries to be.

Raw is recording exactly what the sensor "SAW" while JPEG is doing the post processing that the algorithms tell it a proper photo should be.

Raw takes more time, but post processing a raw file will give a much better finished photo.

JPEG doesn't deteriorate over time, but each time it is opened, any change made at all, and then saved it is recompressed and a bit is lost.

Imagine it as a bottle of water kept in the fridge.

Each time you take the bottle out, look atrocious it, and then put it back there is no loss. However each time you take it out, open the lid to and leave it on the counter before replacing the lid and putting it back in the fridge there is some evaporation because you changed its state.