>>> The problem is some people in their infinite wisdom decided to close the plants for maintenance
The reason is that those plants aren't really in the business of producing CO2. They're ammonia plants, which happen to produce CO2 as a by-product. A lot of that ammonia is used for fertiliser production, which mainly occurs during the winter months, so it makes sense to carry out routine plant maintenance during the summer. Further, the current price of ammonia is so low that many producers view it as uneconomic to restart production at this time.