Because it was a waste of time.
I'm generally against press conferences and other made-up events that are supposed to create news out of nothing. Press conferences are rickety, wizened old antiques from the 20th century. It is all well explained by Daniel Boostin in his classic book The Image: A Guide to Pseudo-Events in America. Press conferences are non-events dressed up as events.
That may have worked ten or twenty years ago when reporters were looking for things to do, but in the modern era when no reporter has the time to travel to a press conference, listen to a bunch of self-congratulatory chit chat, and then drive back to the office, something else must be done.
Conference calls tailored to specific reporters work well. But only if there is actual news worth reporting. That latter part is the tough part. But even if it's only sort of news, if you get a 100-word brief out of it, you've done well since you didn't waste a bunch of time planning an enormously inefficient press conference.
Not all events are necessarily bad, though, if they serve a purpose other than simply restating what's in a press release. The Bianchi Biz Blog has a nice piece here on how to get reporters to those events that are actually worth attending.