We've got insane inflation and she's insisting on tax cuts is what it boils down to. She's subscribing to trickle-down economics which, as is well known, doesn't work. Effectively she's pumping money into a system that needs less money, and even worse she's ensuring that the inflation comes from the top, so it's not that poor people get more money but it's worth less, rich people get more money that's worth less AND poor people get the same amount of money that's worth less. The BoE is trying its damndest to prevent the economy from imploding so it's directly contradicting the government's policies, and it's already had to take some pro-inflationary measures to stop everyone's pensions from being wiped out. The markets are reacting accordingly and utterly shitting themselves, and even the IMF is saying that this is unprecedented. There was a guy from there on the news saying this is the sort of thing they've only witnessed in emerging economies, not mature ones. Truss also told everyone else they need to cut taxes to increase growth.
To sum it up: The economy was heading towards a cliff edge. Rather than put on the brakes, Truss and Kwarteng have decided that the better course of action is the press their foot on the accelerator on the basis that we might actually fly instead. Everyone on the planet's calling them idiots because the economy doesn't actually have wings, but they're insisting that it does. In fact, they've told everyone else their economies have wings and will take off if they just press the accelerator down too, which everyone else ignored because it's insanity.