The first point to make is that not all domestic cats do this and those that do it don’t do it all the time. In fact, in my experience, it is not that usual. But if a cat has eaten enough he or she may try and bury the remaining food. This is caching food for another day and hiding it from ‘competitors’ so that they can’t find it. At least that is the intention.
It is entirely instinctive and inherited from the domestic cat’s wild cat ancestor, the North African wildcat. It is so completely ingrained that it has not been lost over about 10,000 years of domestication but it is a feline behavioral trait that is probably gradually fading away.
Obviously it serves no purpose for the domestic cat in a nice home but that isn’t the point as it is, as mentioned, instinctive and not a rational decision based on the pertaining circumstances.
This behaviour, therefore, does not mean that your cat dislikes the food but that he or she is full up if she has already eaten some of it. It is completely normal.
Below are some links to articles on the topic of domestic cat food which may interest you.