Capitalism has been so successful, it's convinced people that they can have all of it's benefits with none of the pain. That we can achieve advanced technology, bountiful harvests (sans genetically engineered and ecosystem-destroying mass-produced industrial farming), and seeming social stability, without a global system of profit seeking.
I'm not a fan of capitalism. But it's pretty clear when you look at other economies and the state of the world in the past that advancements and social stability don't come cheap. In a post-capitalist society, most of those resources wouldn't exist because there'd be a lack of capital to develop them. Where they did exist, they'd be too expensive for the common person to benefit from them. And where they were applied to the whole society, they'd be ineffective due to poor funding models.
Solarpunk is a utopian dream. We all know how those turn out.