Hashrate is not a relevant measure versus an internal threat. Instead, that is simply a measure to deter external actors like an adversarial SHA256 chain or an upset nation. Hashrate markets allow hashrate malleability, and transitioning from a subsidy-heavy model to a fee-heavy model removes the incentive to behave in an orderly fashion. Misbehavior becomes increasingly profitable as fees increase and dominate the overall block reward.

As for why now, it is a question of risk/reward. As individuals continue to increase our stacks, we become increasingly concerned about risk. Once your stack is at a point where the potential for loss is a material concern, it becomes important to limit risk. Ideally, that can occur by removing tail risk from the project itself, rather than millions of HODLers limiting our exposure to the project.

Considering how many years it took to make a soft fork change like Taproot, I think this is a matter that needs to be discussed constantly. I suspect it will require 2-3 halvings to approach consensus around ways for handling the matter. Plus, I think it is important to have the dialog running so that newcomers to understand that there are aspects of Bitcoin that are far more important and value-add than a hard cap. Decentralization, rules with rulers, and reliability are crucial.