Council law, in Council space, is as solid a governing body you're going to find that spans half of a galaxy and uncounted trillions of people of various species. In the Traverse, where most of the set-pieces of ME2 are placed, the Council is a foreign state, who's laws don't apply.
Back on the Citadel, there's all of two people of any importance who know what really happened in ME1. Councilor Udina and his assistant, Admiral Anderson. Anderson is not a Councilor, he's just Udina's assistant. Udina is a politician, and supremely selfish and obviously a shrewd humanocentric idealist (which, basically, makes him and TIM the same). Udina doesn't listen to Anderson, Anderson has no political clout. All of the Councilors you convinced to help you fight the Geth and Saren died when you let their ship get blown up during Sovereign's attack on the Citadel. Udina has no interest in trying to tie the other races of the Council into a pact of war against an enemy in a region of space they don't control and haven't even seen. It's politically untenable for him, and also provides him with little immediate profit. Not to mention that, in ME2, the bulk of the Council's military might is human, so in a long or particularly violent conflict, Humanity has the most to lose, especially if the enemy is not attacking the colonies of other races. Even if such a war were to come about, Udina may fear that humans would be too weakened by its course to maintain a hold on the political power they had so recently gained. Thus... no Council help for Shep. Udina never liked you anyway.
Basically, there's two worlds at work here. There's however you played ME1, and then there is the "canonical" events that ME2 assumes. I didn't go that route in my ME1 play-throughs, but apparently I left the Council to die, left Adenko to die at Saren's Quick-Krogan-O-Matic lab and punched a baby or something. Whatever, this is the backstory we are presented with in ME2.
Me, I play "Grey Shep", making Paragon/Renegade choices based on whatever I feel is the right choice at the time. This keeps both scores right about the same throughout the game (though does, at times, deny choosing either of their dialog options). That said, Cerberus is not your enemy in the same way that the Geth or the Collectors or the Reapers are your enemy. Sure, you've had entanglements with them in the past, whenever one side got in the path of the other, but they're humans, with human morals, human emotions and human drives. Familiar. Understandable. They have things you can relate to and, if needed, exploit. Cerberus is my enemy only when Cerberus makes themselves my enemy, and they're apparently not enemy enough to pass on spending 4 billion credits to resurrect my frozen corpse *after* tipping of Liara and friends to rescue it from the Shadow Broker, who was going to sell my remains to the Collectors.
Act 1 plays out in the best way that it could have, given the constraints of the game and the fact that it had to be accessible to people who'd never played ME1. Seeing yourself die, your ship blow up, chaos and bloodshed, just to wake up in a laboratory with some weird glowy bits on your skin, is enough to provide the most basic, primary motivation to work with Cerberus: you owe them your life. Cerberus alone has offered you a chance to avenge your untimely end.
There is, of course, the unstated threat that Miranda hints at. She wanted to put in a control chip, but TIM said no. That doesn't mean you don't have a cortex bomb implanted in your skull. They've also got your DNA and a particularly fat file on all your adventures. They could just space-walk you, clone a few million copies, and through neural induction and implanted memories, remake you in the Cerberus image. Eventually, they might get one that works. There's all of 2 returning characters from ME1 recruited into the Normandy SR2 crew... and, to be honest, I almost never use Garrus for anything. Didn't in ME1, either. Like the character well enough, but there are other, better people to fill the role he takes in squad actions. The adventure can get along without him. Having the "real" Shep to recruit these people just makes it easier, not really required.
So, while the idea of escaping the lab alone to return to the Citadel only to find that you've been listed as MIA: Presumed Dead and a brand-new Council that isn't going to listen to you anyway and that ponce Udina firmly holding the reins of power, is interesting and, sure, would have been an interesting, alternate beginning, it really does nothing but add thirty minutes to an hour of travel and cut-scenes to put you right back at Cerberus Lab #2 with Jacob and Miranda and your long-distance call to TIM. From a pacing perspective, and from a design perspective for a player new to the series, I can see why they didn't go that route. It's unnecessary, because you get the same information from TIM, which Anderson confirms if and when you bother to go back to the Citadel to talk to him. If you've played ME1 before, you know that the Council moves but very slowly, and the galactic bureaucracy would tie you up in red tape until the Collectors were knocking on the door before you could even get the keys to a starship.