To grasp the basic idea, it helps to understand how philosophy is organized and how it affects us practically. A philosophy is a unified understanding of Man and the universe that forms a base for our thoughts and actions. It is the source of the principles that provide a rationale for everything that we do.
The core of a philosophical system is composed of three interwoven, primary branches: metaphysics, epistemology, and ethics. Although these are referred to as the "primary branches," it helps to see them as the roots and trunk of a philosophy, or as the foundation. From this foundation, the secondary branches, such as esthetics, economics, politics, education and sociology, are applications; that is, they derive their principles from the foundation (i.e., from the primary branches).
The foundation is critical to what comes after. If you have a really super educational application, for example, derived from an innovative understanding of epistemology, it will work ineptly in a "real world" where most other applications derive from contrary philosophical premises. The same is true with any other application, including political applications.
Political liberty derives from a philosophical foundation that is opposed to the philosophical foundation that leads to statism, fascism, communism or any other dictatorial, oppressive, UNFREE form of government or society. It is based upon a different understanding of our nature and the universe; its principles are different; its application tools and methodology is different.
The liberty "movement" exists within the context of a pervasive world philosophy that is opposed to liberty. In that context, the movement contains contrary, inimical and subversive philosophical premises that color its efforts and goals.
You have the situation where liberty cannot be created because the tools and structures of existing political science derive from an anti-liberty philosophical foundation and so do the values of the people in that cultural context.
Trying to apply some aspect of political liberty, such as a bill of rights, jury trials or representation, in the context where the rest of the tools and the overall framework of government is statist and anti-liberty, will result in sidelining or corrupting the liberty tools. In that context, the liberty tools are incompatible with the rest of the political tools, structures, and purposes, and also incompatible with the philosophical foundation and the other secondary applications.
It is rare that you would get liberty tools at all in the context where an anti-liberty philosophical foundation is generally accepted. And, getting them, it is unlikely that they will last very long, nor, even, that they would be properly identified and implemented to begin with. It is not merely a corruption over time, but a corruption a compromise of principle in regard to implementing them that leads to their failure.