The savings feature is opt in and has no incentive. Especially when the goal is to protect newer or less experienced users, as well as to get a high systemic level of security, this isn't a good combination.

The design of powering up, where you have incentives to do it, and earned stake is at least 50% powered up by default, is built around strong security, both for the individual and for the blockchain as a whole.

Savings is supposed to be a bit more security for mostly liquid funds.

As I said above, I'm not really so tied to the noob security aspect of powering up, but a lot of stakeholders are big fans of it, so I think it would be a challenge ever reaching consensus to allow instant power down.