They were expensive to print and ship, and awkward to lug around—for both PR people who produced them and the journalists who ended up with them. They were bulky, killed lots of trees, and, of course, weren’t searchable.
No one today mourns the press kit, but they were the best technology available at the time.
As corporate websites proliferated, press kits (or at least elements of them) were moved online. Searchability improved, trees were saved, and shipping costs plummeted. Online newsrooms are a dramatic improvement, but even today many are poorly optimized; it’s not uncommon to see websites where the newsroom or media page is little more than a list of press release links, with perhaps a PDF of some media coverage and a few sketchy management bios.
The best online newsrooms combine rich content with careful organization and search capabilities; they enable PR pros to provide reporters, analysts, and bloggers with a vast amount of information without overwhelming them.