Want to know why? The definition of capitalism is "An economic and political system in which a country's trade and industry are controlled by private owners for profit, rather than by the state". This can cause too many problems because it does not talk about who is in control of the "private owners". Only a certain group has power which is not good for those who are not "private owners".
Communism consists of "A political theory derived from Karl Marx, advocating class war and leading to a society in which all property is publicly owned and each person works and is paid according to their abilities and needs". This involves war of the different classes which does cause a few issues. But there will always between people who do not make the same amount or do not have the same things. However, this way each person works to their full abilities and deserve what they make. It is a way to be proud of what you have and to know who is intelligent and who is not.
"If you do not work, you do not eat." Powerful words for which we should be proud of.