In my opinion, the biggest monkey on BTC back is PoW mining and in the end, it will probably also cause it's demise.
Bitcoin mining sector took in 7billion$ miners revenue. That sum will be taken out of the market system and paid by the people who invest with hopes to sell with a higher price. Now, when there will be less new investments then 7billion$ , then the only place to take this money, will be out of coin value. When the miners are no longer able to get ROI, then they will probably start to accumulate and to take on loans to keep their investments running, with the hope of seeing ROI again in the future.
This last part will make things especially fragile and unpredictable. When those mining companies will be no longer able to sustain themselves, then they can't just turn off equipment and live happily. Large facilities have been purchased, workers employed, equipment bought and creditors befriended. In this scale production, your initial business plan either works or you go bankrupt, as simple as that. If you build a factory and you won't get enough demand to continue production, then there is no pausing your production and continuing in better times. The cost of pausing would just be too high for the risk be worth it. Your creditors will want to pull out, and bankruptcy is the only outcome. And if those bitcoin mining companies will go bankrupt, then their accumulated coin, that expected better times, will be dumped on the markets and the equipment will be auctioned off cheap. This will probably cause the final avalanche, that bitcoin won't be able to survive.
Hardcore bitcoin fanatics will defend PoW by trying to compare it to the costs of banking. You can only try to compare those two if you are trying to deceive others or you are totally ignorant on the subject of finance. These two are as similar and different as a paper plane and a F-22 Jet Fighter. What PoW should be compared to, is PoS or newer hybrid systems. It should be compared how much does PoW cost more then those systems, and is there justification with network security for this much higher costs. To ignore this subject is to ignore the most important part of crypto and this is it's efficiency. People ignore it because Bitcoin has switched from being a financial tech project into a religious group. They take Satoshi's white-paper as the holy word of god and they are caught in it's dogmas. Technological progress has switched with religious fanaticism from people who don't care about the tech part or if bitcoin could be actually used as a practical and efficient tool of finance.