Been burned so many times.
Worked for a party that had as its key campaign promise a plan to regulate the car insurance industry. When they got elected, they changed their minds because of the pressure from the industry.
During another campaign the Prime Minister ridiculed the opposition's plan to impose a system of wage-and-price control. When he was re-elected, after a couple of months he announced his own plan to impose wage and price controls.
Liberal parties here invariably campaign from the left (during elections) and then govern from the right.
Right-wing parties focus during campaigns on helping the middle-class; if they get elected they cut taxes to help their rich friends, and help pay for it by cutting services and raising fees - which primarily hits the middle-class.
Right-wing parties often campaign on a law-and-order platform; and once elected, within a few years, lots of their MPs, advisors, and rich friends are discredited for criminal activity - often to do with illegal campaign funding and violations of election law.
Parties campaign on a particular manifesto; when they get elected they pursue major policies that they hid from the public. They had a hidden agenda.
These days it is very hard to believe that they will do what they say. This sort of dishonesty and cynicism undermines the system. And yet I still support and give money to the party of my choice. Go figure!