It was dropped because it was politically impossible and it wasn't worth burning political capital on it. Even just the public option wasn't able to gain traction; single payer was never going to happen in 2009.
And then watched it get blown away by next congress as soon as the GOP gained 51 seats to do whatever they want. Blowing away the fillibuster is an awful, terrible, no good idea and there is almost no legislative agenda which would validate it.
And to be clear, the GOP senators were and still are slimey bastards for basically everything they did leading up to Gorsuch. It should have never been done. They will almost certainly regret it as soon as they lose the senate.
Public option is a great solution, because it does not prevent the people who prefer (and can afford) to pay for private services from doing so.
And that is counting Lieberman as a D; a person who backed McCain for president and who later personally killed the public option.
I do think we will get to the public option at some point. It just makes too much sense not to and would strengthen the healthcare as a whole while allowing people more choice.