Which principle of Public Relations 101 prevents Amtrak from spreading good news in advance? Press releases can't be that expensive.
Unless they cost you in bad PR. Amtrak might be unsure of the date the lounge will actually open. A press release promising something that turns out to be not true would be worse than no PR at all, IMHO.
That leads you back to another principle of Public Relations 101... under promise, over deliver. People get frustrated when you miss a deadline... but nobody's mad when you're finished ahead of schedule.
Amtrak could simply say something like "expected to open late summer" or "expected to open this fall." You wait to give the exact date until the project is finished.
But the lack of a specific date shouldn't keep them from sending out a release and some images (a rendering of the design, photos of construction). Amtrak is missing out on an opportunity to build public awareness and excitement for the project (outside of our railfan circles.)