Why don’t producers inform cast and crew before press releases go out?

Call_me_jorge said: "The Dear Evan Hansen West End production sent out a press release saying they dont plan to reopen until next year or when its practical to do so. It appears that the cast found out at the exact same time the public did. Then there is what is going on with the London production of Phantom where cast members are finding out stuff from their social media. Im just curious what is stopping productions from communicating with their casts before going public with certain information. I understand that technically none of them are currently employed by their respective shows, but it just seems to lack common decency."

Because the press team wants to control how that news is delivered and by whom. If you tell the cast in advance, it will almost certainly leak and then it becomes much harder to control the narrative. Remember that the producers are fighting tooth and nail to keep shows alive, which is in the best interest of everyone working on the show, including the cast.

That being said, If the cast is finding out from news stories that is unacceptable and disrespectful. They should be hearing things like a new planned opening date directly from the producers, via an email sent out around the same time that the press is notified.

This is just PR nonsense. Read what it says. It is not announcing anything because no one knows anything. The show will open when it is practical. Wow what a news flash. I wish folks here would accept the fact that everything stated in all of these situations is meaningless and not made more likely or not by a press release. The purpose of a press release is to keep you name out there. What are cast and crew supposed to be notified of? That the show is keeping its name out there? (And yes, the key is as itsjustme says that if you tell actors anything it will be on social media in a millisecond and you've lost control of the narrative. Again, let me repeat: patience. 

Back when I worked in the industry, the box office called me to tell me a particular show was closing in the morning, and the press release wasn't sent out until the afternoon. It's crazy, it's sad, but it's the nature of the business. It's show business, and that means nobody wants to set up a Zoom meeting, then have people on that call be like, "Uh oh, cast meeting in a hour!" and set social media ablaze in speculation.