Colorado police officers Leave patrol car with suspect inside on train tracks in path of train

Because it's the domino that actually fell down. Once the criminal case is complete, the city will keep looking out for their own best interests, which in this case means terminating her. If, by some chance, she was found not guilty the city could use both the not guilty verdict and her current employment as an affirmative defense. Please see the Michael Bell Case where the city kept the case going long enough that the statute of limitations ran out on most of the charges needed to prove gross misconduct.

If you look at most egregious police misconduct cases, they follow the pattern of "We have to wait until the court cases are done with before taking employment action so we don't influence the court case". If the criminal charges are unsuccessful (or are never filed), the officer remains employed (or just doesn't get fired) until the end of the civil action. If convicted, the officer gets fired because the conviction is admissible. How would it look if the officer is convicted of misconduct but not fired? When asked about the delay, the answer is "we wanted to let justice prevail first" or some such nonsense.