Most likely, there are discussions going on in the background with the League, Equity, other unions, producers, the state/city, etc on a number of issues that as many people as possible need to be on the same page for. Things like income for actors/stagehands/musicians/etc, how to divide up stimulus money, the projected future of the virus etc. all need to be taken into consideration. Productions in previews at the time of the shutdown need to set a new opening night (which requires coordination to try not to have two open the same night)- or if to open at all. Other productions need to figure out how quickly (and in some cases, if) they can open again.
Not to get political but Trump's desire to have the country reopened by 4/12 may be a factor. Once some states/cities open, the virus will hav a chance to start spreading again, making "stay at home" orders in other places less effective, and therefore less defendable Also, while Trump may not be able to force states/cities to lift shutdown orders, he CAN make it difficult for them to remain in place. For example, he could limit funding supplied by the executive branch (FEMA, etc) after April 12 (or whenever). At a certain point, there wouldn't be much of a choice for NY to lift the shutdown. Its conceivable everyone's waiting to see what the feds decide to do.
All that said, we are coming up on two weeks until the planned re-open date. Things are going to have happening soon if re-opening is going to happen (cleaning the theaters, perhaps some run-throughs, etc). People holding tickets for soon after the planned reopening need to be able to make plans. I'm supposed to have a Broadway weekend May 1-3. I know it's unlikely my plans will go forward, but would rather not be running around at the last minute to cancel the train tickets and hotel (and don't want to cancel only to learn the shows are going on). People with tickets for the week after Easter have a tighter time frame. Decisions need to be made, but we should remember there are a number of groups involved, and its preferable (a) to have a consensus and (b) come up with a date which is realistic, but does not push the date farther back then necessary.