Why does saturation occur?
Every solvent (e.g. water) has a specific "power" to dissolve a specific solute (e.g. salt). Imagine adding sugar to water, if u add a little amount, it will still dissolve, but if u keep on adding and adding, then it will pass the solvent's (the water) "saturation point" resulting to your sugar remaining as a "solid". So, saturation occurs because the capacity or power of a solvent to dissolve a solute has already been reached.