In general I think people underestimate how volatile politics is election to election.
When we look back we see that things have changed a tonne over the last 5 years. But then there's a tendency to think the next 5 will be more stable because we can't foresee how specifically it will change.
I've been around long enough to hear "this government / new political equilibrium will last for a generation" many times, only to have it fall into disarray a few years later.
When you're forecasting many years out, you need to keep in mind how many strange and unexpected events can accumulate over that time. And that voters tend to sour on whoever is in power, which limits how stable things can be.
One driver is the media wants to make anything that happens seem momentous in order to keep your attention.