Erm, most when dark without user input from my perception, when I looked at the list, and the subs, there were both no surveys and no time to gather input from users, subs were already committed before most knew of the plans.
In the couple subs I'm involved with, one of which animal health is involved, I considered bringing up having a poll to follow what users would want. But then also realized users could simply not post to participate.
Instead what happened is the loaded "are you going to join the blackout" imagery and post that was spammed all over reddit got posted. It was interested as universally all the comments were bandwagoning despite the health impacts to animals. It was also interesting I had to keep approving the post as so many reported it.
Then during the blackout most didn't even know it was going on (because hiding isn't an effective way of getting a message out obviously). Many thought they were kicked from other subs and our sub ended up being a resource for health in like of similar subs being closed. Some alternatives to those subs were getting traffic too. None of those subs had polls asking users their desire.
Very few polled users from what I saw, and of those, often the polls were not objective but loaded, without context.
Users did turn to other subreddits, front page had posts that would've been in regular subs being posted in previously unheard of subs.
What's extra crappy is if any sub closes while in a private condition, it breaks google links to info, whereas most users contributing info want it exposed to others, and if they don't, can affect that choice themselves instead of having others dictate it for them.