The Fifth Amendment to the Constitution reads as quoted below. It also applies to State takings through the adoption of the fourteenth Amendment.
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a grand jury, except in cases arising in the land or naval forces, or in the militia, when in actual service in time of war or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation."
The issue you have is not the compensation, but rather what constitutes a "public use".
I am not going to provide you with a legal treatise. However, the various courts of this land do not agree with your view of public use. An activity need only be found by the legislature to be publicly beneficial to meet the public use requirement.
Thus, to be able to take property for just compensation, all the legislature needs to do is empower a public agency to condemn property and purchase land for some project that the state views as beneficial to the public, and it is a "public use".
Under this view of things, private property has been condemned for housing projects, industrial parks, utility facilities, airports, railroads, etc., things that you might view as private activities.
Therefore, if the legislature finds that the public interest is served by setting up an industrial improvement authority, and that authority seeks land to build an industrial park to be occupied by private firms, the industrial improvement authority may indeed be empowered by the legislature to condemn land for that purpose.
In some cases, such as public utility corporations, the state condemnation power has even been delegated by the legislature to private corporations to exercise on their own.
Can you cite me any examples where the public taking/just compensation provisions have been expressly used to take private property to turn it over to a car wash operator?