Blink 20's come from Blink users using points to "purchase" site visits.
Since the level of points earned daily is down, there are fewer Blinkers able to cash in for site visits, so therefore Blink 20's will be down.
20's used to show up almost every day, then it dropped to about 3 days a week, then two days a week, then one day a week, now it will probably be every other week.
At least that's my theory on the situation.