It was cut in order to entice the for-profit hospitals, whose support Obama and the White House believed was necessary to pass the ACA. A public option would reimburse them at lower rates than private insurers, and so was a threat to their bottom lines.
Daschle: Public Option ‘Taken Off The Table’ In July Due To ‘Understanding People Had With Hospitals’
In his book, Daschle reveals that after the Senate Finance Committee and the White House convinced hospitals to to accept $155 billion in payment reductions over ten years on July 8, the hospitals and Democrats operated under two “working assumptions.” “One was that the Senate would aim for health coverage of at least 94 percent of Americans,” Daschle writes. “The other was that it would contain no public health plan,” which would have reimbursed hospitals at a lower rate than private insurers.
Obama Is Taking an Active Role in Talks on Health Care Plan
Several hospital lobbyists involved in the White House deals said it was understood as a condition of their support that the final legislation would not include a government-run health plan paying Medicare rates — generally 80 percent of private sector rates — or controlled by the secretary of health and human services.
“We have an agreement with the White House that I’m very confident will be seen all the way through conference,” one of the industry lobbyists, Chip Kahn, director of the Federation of American Hospitals, told a Capitol Hill newsletter..
It should further be noted that this was done in secret, while Obama was still promising the public option to the public.
Several bloggers and reporters compiled the evidence but my search started with this post by Glenn Greenwald, which has a comprehensive compilation of evidence, or links to compilations of evidence, or links to links: Truth about the public option momentarily emerges, quickly scampers back into hiding.
(I don't know whether it is faux pas to respond to really old questions but I think this answer is more direct and accurate than all the rest.)