Alicia Marcus: I still own 50% of this company.
Dr. Isaacs: And what do you intend to do with that?
Alicia Marcus: You are co-owner of this corporation, but Wesker... Wesker is still an employee.
Wesker: I don't have to take your orders. My loyalties are with him.
Alicia Marcus: I know. Albert Wesker, you're fired.
Dr. Isaacs: We've played a long game, you and me, but now it's over.
Alice: Yes. Yes, it is.
Dr. Isaacs: I made you.
Alice: Yeah. Big mistake.
Wesker: Help me.
Alicia Marcus: You don't need help, Wesker. You're dying. Just get on with it.
Alice: Sometimes I feel like this has been my whole life. Running. Killing.
Alice: My name is Alice, and this is my story. The end of my story.
Answer: In all honestly... this film series isn't one to shy away from ret-conning elements of prior films. ("Ret-con" being short for "retroactive continuity" - a storytelling device in which rules and plot-points are either changed or ignored in later installments.) This just seems to be another example of a ret-con. The idea that Alice was the "cure" all along would have ended the series a lot sooner, and they wanted to make more movies, so they just sort-of "ignored" this idea in the sequels that followed "Extinction."
TedStixon