why does the alpha in Louvre don't kill itself?

Rating: 8/10 (7 June 2014)

In the end of the film,the alpha in Louvre just follow the Cruise and kill him.
But it's too late,made Cruise's mission succeed. Why did it just kill itself ? It can trigger Omega rest time. Then defense Cruise's attack.
Cruise has lost the ability to remember. It can save the Omega's life.
It's a big bug! The alien's IQ was so low? May be this is the only reason can explain this...
I want to talk about this in here, is there have any better reason to explain this?
The director should set up a alien who has no reset the ability to kill Cruise to solve this problem.