I work in a place that has a pharmacy distributing the J&J vaccine and from what I've heard they've been getting about a third of the doses they're supposed to be getting. I rarely see people in to get shots. The governments are desperate to get things opened asap (think kids back to school, summer recreation, tourism, etc.) The governments' initial timeframe had the vaccine rollout taking all summer. Then the J&J vaccine begins going out and suddenly a bunch of states abandon their rollout plans, turn it into a free-for-all, and begin subtly projecting an "end" to the pandemic in May or early June.

My theory is that for multiple reasons, J&J and/or state governments ridiculously overstated their capacity to produce and distribute this vaccine and are now trying to cover their asses by saying distribution is stopped because of potential side effects rather than their own incompetence and the extremely limited supply. This would explain the issues of getting them and why a less than one in a million chance of a high risk demographic developing blood clots is enough to justify pulling the vaccine.

I also suspect they realized they can't safely open schools like they've been promising (a local high school made it four days before COVID started spreading). While the J&J vaccine is not yet approved for children, I think that they were counting on a sort of adult herd immunity to make schools safe enough to be opened until vaccines for children are distributed. Since a massive chunk of our vaccine supply is now considered unsafe, they have an excuse to reverse their position on schools opening (which was incorrect, it was not safe for children to be in schools).

Essentially this whole thing is cover for the government to reverse their position and announce what has always been the unpopular truth: that the pandemic will not be over for at least the summer.