Progressivism is a collectivist political ideology that intrinsically rejects the idea of a stable Constitutional order in which government power is defined and limited, and process and procedure are elevated always above desired outcomes, regardless of their popularity.
Instead, Progressives begin their worldview with the proposition that the rights of citizens are defined not by God or human nature, but by government. For the collectivist Left, the overriding purpose of government is not to ensure liberty or property rights, but to pursue "equality" or "justice" in myriad forms, militating toward equal outcomes in all human endeavors.
Such outcomes are valued irrespective of individual ability, effort, or desire, with government performing an active role in ensuring such ends, most often through redistribution of goods and services from those who have greater amounts to those who have less.
The means by which these ends are employed cannot therefore be limited by processes and procedures that serve (for the Constitutional conservative) as necessary constraints upon government power.
By extension, and for those who desire the Progressive ideal of society, this means that a firm Constitutional order cannot survive where the primary purpose of government is to ensure equal outcomes.
The very purpose of a Constitution is to establish government legitimacy, by defining and delimiting the structure of government and the powers of its various elements, by establishing processes and procedures for political representation and redress of grievances and by providing a mechanism for future changes.
All of these things are anathema to the Progressive, which is why they always and everywhere seek to avoid guardrails that frustrate their Utopian visions in the abstract sense, and their desire for power over others and access to their wealth, in the practical one.
Finally, political Leftists have had a demonstrated ability to enrich and empower themselves through both political intrigue and promises of unearned benefits to dependent constituencies.
These are the true fruits of a Progressive ideology that always fails as Utopian ideal, but given the imperfections of human nature, often succeeds as a practical means to even transparently corrupt ends.