Much of it also depends on the lessor. Remember most airlines don't own the bulk of their aircraft so for many they're not the ones making decisions about where they go.
Anybody who says "X aircraft won't be back until Y" is also really just crystal ball gazing. The reality is none of us know what the world will be like 6 months from now.
Air NZ had (from memory) 2 of the 77Ws that had leases expiring within the next year and have already taken a huge financial impairment charge ending the leases on the leased 772s so if any do come back they'll potentially only be the company owned frames.