Although PoW has its benefits, besides being the best known method, it also has its own inherent challenges. Nodes need to use real-world resources, such as computers and electricity. It takes a lot of power to run the computers, or clusters of computers, that calculate different potential solutions, which from an ecological standpoint isn't ideal and it is bad for the environment as well.

The nodes need a lot of computing hardware to reach a consensus and such hardware is really expensive. There is a possibility of miners moving their hardware to mine a different coin or an old coin if the reward is better there. In this case, miners and nodes are less loyal. PoW incentivizes the consensus process, which is a motivation for miners to mine blocks and earns rewards. However, with the maximum capacity of 21 million Bitcoins, with more and more points being released over a period of time, miners' rewards will come down as coins become harder to mine. This may lead to demotivation for miners to continue mining, which might challenge the overall consensus.

The fact that you need a serious amount of computing power, more than the average person could afford or would even be able to work with, means the mining community is getting smaller and more exclusive. This goes against the idea of decentralization and could potentially lead to a 51% attack.