People are frustrated with experts because we've delegated increasing amounts of authority to them while our life expectancy and incomes drop. Alan Greenspan was an expert. Dick Cheney was an expert. Experts told them that NAFTA would be a huge job creator in the US while certified crazy man Ross Perot said there would be a "huge sucking sound" of job loss. One of them was right about where the wealth would be going.
People feel like they have less control over their lives and less power in their democracy than they used to. Political power is increasingly consolidated into smaller and smaller groups of people while our lives are largely dictated by large corporations. As people lose agency, they're going to distrust the idea of placing more power into the same hands that got them there in the first place.
People are frustrated by idiots/people who are intellectually dishonest implementing policy and framing narratives on how society should tackle challenging problems. Many of their making. Think of the kind of mix you have at say the European Commission, the ECB, and the IMF. Then look at what they facilitated in Greece. Onr of deepest and prolonged contractions ever recorded.
There's simply too many people with credentials doing dumb things or being plain evil with zero shame. Eroding faith in institutions through continual incompetence.
Alternatively, think about the US where manufacturing has been hit hard, wages have stagnated, and economic mobility isn't where it needs to be. Health care is taking up too much GDP. College costs are out of control. The retirement system is a big fat joke. These are functions of policy and ideology with an intent to stack the deck. It hasn't always been this way and it's not an accident so many folks are losers.
It's not about control. It's about seeing incompetent people who utterly fail at what they do refusing to retreat, refusing to retract, and doing everything they can to avoid admitting mistakes. The folks who burn the house down think they should stick around and lead the clean up. We've entered a political climate where that can't fly. Thank the irreparable damage from the financial crisis for pushing dummies out and putting who's left in power on defense.