I remember way too much random crap in meta...
If the feature was written as:
-For every thread page of 20 posts that someone views:
-for every user that posted:
-look through every other user's ignore list and add up the times that user has been ignored
That's basically how it works because the ignore mod (which I didn't write) stupidly stores ignore info in a single column per user like "35,3,...". So each ignore button needs to scan through all established users. The cost of this used to be very little, but it has increased substantially as the number of users has increased. I added a lot of caching long ago to offset this, but the cost is too high now even for that. I need to mostly rewrite the ignore mod so it stores data more sanely. No too difficult, but it requires a somewhat large uninterrupted block of time, which I don't have right now.
tl;dr It's disabled for now because of being too processor intensive.
