It's 80:20 isn't it, the big subs are the draw, so they probably only need to force those to open to get traffic back. They can probably afford to pay for mods on those subs, as for the smaller subs, they probably don't care.
But if the 30 small subs I frequent all go elsewhere, my eyeball time on Reddit is going to go down significantly. Each of those 30 subs might be a tiny slice of my overall use, but together they make up the vast majority of my time on the site.