Because... that's not true.
Energy being cheap does not mitigate the problems created by climate change, and there are many scenarios in which low prices make climate impact worse, such as oil prices falling and consumption increasing.
It'd be nice to talk about this stuff in terms of prices because they're very convenient, but convenience does not necessarily make a good metric. The price shout-out is like an ancillary observation at best.
Cheap energy is a great way to solve a lot of the other problems. And lower carbon energy can chip away at the root cause.
I have some hope that we're starting to turn the corner as birth rates keep going down, and I am somewhat hopeful that things like renewables will keep pushing forward and contribute to helping us move in a better direction, but there's still a ton of stuff that won't be helped. You can't eat cheap electricity provided by solar panels, at least not in any sort of regime that feels believable (I don't think giant fields of green houses is a plausible replacement for modern intensive agriculture), and it still relies on all sorts of manufacturing processes that are in no way sustainable. That hope runs up against proclamations from people like Musk and my local government that WE MUST GROW at all costs. We need to triple our population by 2100 despite the fact that our infrastructure is already groaning at less that half the goal. I think its pretty clear that there is no sustainable QUALITY of life at 9 billion, and I can't see it being feasible anywhere over 5 billion, maybe. But the powers that be in society see that they could reign over a teeming mass of the impoverished and I truly get the feeling the sentiment is our billionaire class would rather reign over a ramshackle society of poverty where the gulf between them and everyone else is titanic instead of a sustainable society when the objective standard of living is higher but the gap is narrower, and so I'm not sure if we'll actually make any moves to improve things or just slowly work our way to a grinding cyberpunk dystopia.
To summarize, it feels like people dunking on Malthus and Ehrlich are whistling past the graveyard, their stomach full of seed corn allowing them to put off thoughts of the future and all that matters in our society currently is the next quarter's results. Winter is coming and its not going to be pretty.
> the green revolution allowing us to feed people by basically converting petroleum products into agricultural yiel
The green revolution was largely about shuttle breeding in wheat, corn, and rice. Higher yields mean less land can be used for agriculture. Were we see most biodiversity loss and deforestation, people are subsistence farming, engaging in slash and burn agriculture, and using unimproved seeds/methods.
> You can't eat cheap electricity provided by solar panels,
You can split water and force the H2 under pressure to combine with atmospheric nitrogen and create 0 CO2 fertilizer. So you kind of can eat cheap electricity once its cheap enough.
> that WE MUST GROW at all costs
Economic growth isn't tethered to land use anymore and is increasingly detached from CO2 emissions. A few centuries what little economic growth that existed required grain and wood. Economic growth makes us richer, and that extra accumulated wealth allows us to do things like environmental protections. You see the world over, as countries become richer they devote more resources to environmental protection.
> I think its pretty clear that there is no sustainable QUALITY of life at 9 billion
That isn't clear at all. Paul Ehrlich predicted that 6-7 billion people would lead to mass starvation, yet food insecurity is at an all time low. The Club of Rome predicted we would be out of resources by 1992. You're making the argument that people made about the end of whale oil. The mistake is that thinking resources are fixed and finite arrangements of particular atoms in the ground, rather than the application of human ingenuity to raw inputs. Oil was originally useless black gunk.
I'm not denying that there are problems and that there will be consequences of the old carbon economy. I'm not saying that habitat loss isn't a problem. I'm am however pointing out that these are solvable problems and a lot of very capable people are hard at work. Low and no carbon energy is now a solved technical problem and has become merely an infrastructure challenge. That's pretty amazing. Agriculture isn't standing still, there are a ton of gains to be had in land use. Society has managed to solve a lot of hard problems, we have the ability here.