I don't understand why they would want to allow current subscribers to renew and not allow new subscribers to start up.
Only thing I can think of is that they may want to announce the departure of the new tools soon, to happen sometime over the next 18 months, for example, and they want to stop taking on new users, but preventing current subscribers from renewing right now would cut off people immediately whose subscriptions are due to expire before they can make their announcement, which would be bad all around. Instead, if they want to phase the tools out, it makes more sense to make sure everyone who is a current subscriber gets the use of the tools for the full term of the subscription so there are no refunds that have to be given.