Looks like it can have adverse side effects and it's very easy to overdose, leading to fatal organ failure. Also several factors, like existing medication or just consuming grapefruit juice, can affect concentration in the body.
If my understanding is correct, it's to be administered early, after a positive PCR test. But only a fraction of the infections lead to hospitalization with serious symptoms. I don't know the numbers, but let's say, if 10 people die out of 10000 because of COVID, what's the point in taking the med if 10 people also might die because of it?
https://en.wikipedia.org/wiki/Colchicine