How do you come to that conclusion?
Because a "sustainable" way of life is one that every single person on the planet is able to live (in theory at least) without affecting the ability of future generations to also achieve that same life.
What we in the West have done so far is that we have created a lifestyle / standard of living based on a stunningly huge amount of fossil fuel extraction and use - and by ignoring (externalising) the environmental impact of what we are doing - by exporting it elsewhere or just turning a blind eye to pollution, resource depletion, species extinction, loss of biodiversity. And we haven't just done it do we can have indulgent "fun" stuff. That's what it takes to provide the things that we consider to be basics - roads and motorways, transport infrastructure, schools and hospitals and houses and apartments and universities and factories and offices etc etc. It's also what we do to power the things we use everyday: cars, buses, trains, boats, planes, factories, lights, gadgets, IT and telecommunications infrastructures. We've developed a lifestyle and associated expectations based on the old idea that resources are infinite, that we would never run out of them, and that the environment (air, water, earth) could endlessly absorb whatever shit we put into them - as long as it didn't cost anything.
And that's before we even get into the fun stuff - travel, holidays, toys, gadgets, media, etc.
So... if providing the "basics" to the small fraction of the world's population that lives in the West has created the environmental catastrophe that has been revealed to us in the form of climate heating... how do you think we can provide these basics to the rest of the world - to the populations of India, China etc who want what we've already had? Who want suburban houses rather than slums / wooden shacks / 15 family members in a 2-bed apartment? Who want running water rather than a shared village tap? Who want electric lights rather than paraffin lamps? Who want roads and trains and a bus service rather than potholed tracks and a diesel rickshaw? Who want a car of their own parked in their garage rather than a smelly minibus that they share with a dozen other people?
And how on earth do we then ensure that not just people alive on the planet have access to a "basic" standard of living... but also ensure that future generations are able to achieve at least this standard? Clue: we can't.
That's why no one is telling the truth about "radical" change.