[Brighthurst]

From a theoretical standpoint, this answer could get very long, but the real answer boils down to the creator of the protocol prefers bitcoin.

On the theoretical side, I'd argue that bitcoin PoW is the best choice because it is more resistant to malicious actors. Assuming that a solution to the botting issue requires a small proof-of-work or fee to post, on a PoW chain malicious actors would need to control a large amount of energy inflow and hash power to support their botting operation. Whereas on a PoS chain, they simply needs a large pool of capital to be staked, which would give returns that can support their operation. This means that the attack vector is larger on a PoS chain than a PoW chain. This is also why the nostr protocol itself has a proof-of-work component. It's the simplest solution to two-generals problem.

[Edes]

Proof of work also depends on capital, compute isn't free. In fact, it is already incredibly centralized in the Bitcoin blockchain because there's like 3 big players which have already attacked the Bitcoin Cash blockchain. The only reason these huge pools haven't attacked the Bitcoin blockchain is because they have a financial stake on the price being high, which is also the same incentive proof of stake depends on.