Because without the right to create, own, protect, and dispose of property, there is no society and no Human good, and if you look around the world today you will see that to the extent that property rights are respected there is a better standard of living for everyone and where they are not, to the extent that they are not, there is misery. Just look at North Korea vs. Hong Kong. Look at West Germany vs. East Germany before the wall came down.
The founding fathers could have easily listed property rights along side life, liberty and the pursuit of happiness. They didn't need to because property rights are implicit in all of those other rights. Your first property is your life. If you don't have a right to property then you don't have a right to your life.
Property rights are not a primary. They rest on man's individual rights which are not handed down by a deity or society but are inherent in man's nature. They are conditions of existence required by man's nature for his proper survival. It is helpful in these kinds of issues to look at the fundamental principles. The fundamental principle of individual rights is that man has a right to live for his own sake. The fundamental principle of collectivism/socialism is that man has no right to live for his own sake but must live for the group or the tribe or the society. By placing the group as the standard then each individual man becomes a means to the ends of others and a sacrificial animal and that is what you find in every society that places the group over the individual. Hundreds of millions slaughtered in the 20th century alone.
Don't fool yourself as many do by rationalizing that the fundamental principle of collectivism is a noble principle that was corrupted by Hitler, Stalin and Mao. It is the principle itself that is corrupt and Hitler and his fellows practiced it the only way it can be, by turning the world into a sacrificial furnace.
