Because governments of any size are largely run by bureaucracies. This is both positive and negative in that it's stabilizing, but also can become anti-democrat

Because governments of any size are largely run by bureaucracies. This is both positive and negative in that it's stabilizing, but also can become anti-democratic and parasitic. The politicians in the modern Western world mostly just give speeches and make deals and go to meetings. Sure they can guide policy to varying degrees, but implementation is through the bureaucracy. I have to imagine when a new leader or parliamentarian comes to town (if they haven't been in town for years already and know "how things work") they are immediately set upon by a plethora of advisors and "experts" who explain reality and what must be done. The politician then most likely see the light, but if not, they proceed to run into massive difficulties and very probably won't be there long. I'm only familiar with the system in the US, but I think this explains why people vote for something, then none of it happens, even the reverse.