My short answer is that because of materials and engineers. Now I will tell you a long story. It is not the first time the green revolution has failed. So, it is not actually a big deal. Just like the failure of Steve Jobs in "Next" staged the next Mac revolution, failure is an integral part of success and development. You only need to understand why it happens.
The first problem is to understand how this green transition is designed. If we look at the oil transition, it started with engineers. They analyzed, invented, and designed systems. In gas and LNG, it is the same bottom-up process instead of a top-down one. As far as I know, only one transition happened top-down: France's Messmer Plan for nuclear. In that case, the engineering capacity was there, and the plan created the scale of the project. However, it still took lots of debt and years to switch one resource.
The current "mega transition" is mostly designed by economists, politicians, lawyers. They decided that all four energy resources (oil, coal, gas, and nuclear) should be out of the picture. On the other hand, some of these people were also associated with certain NGOs (Non-Governmental Organizations). These NGOs' incomes were mostly sourced from environmental or climate projects. Hence, a conflict of interest occurred when pushing more for these policies led to increasing rent and income. This eventually caused new policies that lacked public support. In some cases, the public was the only one who did not need to change, transform, and suffer from the adverse effects of transition.
If people need more evidence to be convinced, one can calculate a high enough pollution price that justifies everything for the short, medium, and long term. But at the end of the day, these policies affect people's lives, and their implementations are feedbacked by the harm or benefit of the people's experience. A politician can warn people about the urgent danger, but the near-term benefits outweigh the long-term harms.
The other problem is the paradox of material requirements. You need to have more copper, aluminum, steel, glass, cement for the same amount of TWh/year generation. To meet the demand, you must mine at least some of them. All these operations require huge amounts of energy, whether green or not. In the end, you either choose to consume this energy to produce more materials for renewable systems or not.
The current transition aimed to close all oil, gas, coal production in 30 years by replacing them with more solar and wind. Empirically, renewable investments surge during low oil and gas prices. Since it is cheaper to produce materials and economic activity is generally higher during low energy price periods. It is counterintuitive, but renewable transition speeds up during low energy prices. Thus, closing all fossil investments also increases renewable system costs.
Demand is another big issue. The energy density we consume is huge. A liter of diesel is 10 kWh of energy. You can carry it store it; in the worst-case scenario, you can burn it. However, renewable energy is sparse intermittent. Fossil fuels are like a pond, and renewables are like water harvesting devices from ambient humid air. Still, we need the reservoirs for our water needs. Water harvesting cannot feed our thirst for water. Still, it is very useful.
Another problem is fatalism. Yes, there is urgency but constantly alarming everyone will lower their risk threshold. It is basic PR. You do not need to read any doomsday news nowadays. The plot is simple, we are all doomed and will die, but our experience shows that you need to make people focus on a few things instead of the whole issue in times of urgency. One step at a time is the best way for stable progress. So, we should also increase renewables as much as possible.
Frankly, we do not have enough economic, mature technology options other than solar and wind due to huge energy systems from cars to factories, electric systems to refineries, gas, electric grid systems. Up to now, oil supply chains are the most complicated machines humans have ever created. The technology of renewable energy systems requires innovation. This takes roughly 20 years, from labs to markets when planned seriously. Talking the talk is cheap but walking the walk needs a lot of effort. R&D budget commitments should surpass other R&D budgets if we perceive the transition as urgent.
We should go back to the drawing board to do all these transitions. We should try to chew one piece at a time. This stability will foster more confidence and create a snowball effect. Ambition is a poison; soberness is the way forward. Yet we should remember that this is a transition to be achieved by engineers. From designs to digital systems, materials to mining, power systems to hydrogen, energy efficiency to nuclear, you either have it or not. As always, their transformation will determine the speed of transition.