In this context, "consensus" means agreement about transaction order, not the state.
In case it is not clear, nodes can agree on the result after they agree on transaction order because they can work out, independently, what the state must be. It's similar to a replay log that enables reconstruction of a database.
Nodes learn about proposed transactions at different times due to network latency. Given that no one's clock is any more authoritative than anyone else's in a decentralized system, timestamps are not a solution to transaction order. If the goal is that no node is more authoritative than any other, how then to assign the privilege of deeming the contents of each block?
PoW makes it computationally expensive to gain outsized influence over the system. It can be thought of as a resiliently randomized election process. PoS is an alternative method that attempts to accomplish similar goals with improved performance.
Hope it helps.