I think the most likely explanation is that Bioware didn't finish the story to do what the lead developer said he wanted, to have an ending people would remember (a terrible one that makes no sense where Shepard is clearly just imaging it all while being indoctrinated) and plan to finish it with DLC. Which is probably why they said within a couple days that they knew people hated the end, were thinking of changing it, then were changing it, after they already said the next free DLC would add more to the story anyway. Most developers go on vacation when a two year project is done not agree to rewrite their ending a week after release. @nutcrackr It's a pretty short game
Just like so many other people, I did not like the ending to Mass Effect. The final explaination to why the Reapers were killing off everyone so that way they could prevent artificial intelligence from denying future organic life development in the galaxy. If I were to have control the story of Mass Effect how could I reorganize the characters and storyline so it made more sense?
The reapers is an all powerful entity expanding to more then one hundred other galaxy across the universe for over a billion years and their goal is to allow rise and fall of advanced space faring civilizations and prevent over domination by interfere the development of other races that have not yet achieve faster then light travel (FTL). They would have created Mass Effect relays, the Citadel and other structures to attract advanced civilizations by giving them two laws. The laws is advanced warning in preventing the civilizations destruction. The reapers dont interfere how each races deal with each other, like if one is at war, developing genophage, or organizations like the Alliance.
50,000 years ago the Protheans and an artificial intelligence created by the Protheans were at war with each other. Both parties were the most dominating and advanced of anything at that time and the reapers allowed them to continue until their conflict got so out of control it would have effect other non FTL development. This led to the sudden disappearance of both races and the sudden rise of 23 races across the galaxy from left over Prothean technology over the last 1,500 years.
Asari was the first to advance then shortly after four others. The Alliance was established by Asari and the four other civilizations joined in. Five more joined over the course of a thousand years, while 13 others were aware of the alliance existance by did not take part of. The non members were still allow to travel to the Citadel, take part in trade, communication and make residence. The citadel and a near by planet it is orbiting, is home to more then 4 billion of mixed races across the galaxy.
Humans is the newest member of the Alliance and the relationship with each race was mixed. They were friends with Asari, Quarians, Turians, and Salarians. The worst enemy was the Collectors who saw Humans as invaders, because Humans had quickly increase its territory in the galaxy. Mining and colonies were attacked by Collectors including joint Turian and Human installations which caused both to take cause to stop them.
Shepard is a newly founded commander and comes to Citadel as all other races look down upon him. A rogue Taurian leader along with Drell and Vorcha targeted Alliance infracture throughout the galaxy including the attempt to kill all of the council members until Shepard pushes back. The rogue Taurian leader along with is generals are killed the day is saved by Shepard causing the trust of Humans enough to join the Council.
The Collectors troubles began to escalate to the point where war was evitable. Shepard is there to stop the Collectors from attacking Human settlements to prevent all out war. They search for the leader of the Collectors who are responible for the push and kill him at the end. Killing of then instantly stops the Collectors attacks toward Human colonies forever.
The Collectors five years later became ultra aggressive and effected two non FTL civilizations. The Alliance was suddenly alerted for probable trouble from the reapers. Shepard mission was liberate one of the planets collectors are attempting to capture, warn them about the reapers, and even align at least nine races in the galaxy to defend the collectors from the reapers. At the end of Mass Effect story, it would show humans as being able to forgive and take pity to a known foe and this caused the collectors to end their aggression. The whole point of Mass Effect storyline would for Shepard show great leadership and help prove human unique role in the galaxy while other races might not show.