Because it doesn't matter who you cast in Altered Carbon season 2. Joel Kinnaman absolutely nailed it in season 1 and while I understand the story of why he is replaced, it just doesn't work. No one could have taken the role. Not that Mackie did the role any favors, but it was an uphill battle from day 1.
Kinnaman nailed the roll. season 2 had so many problems that I don't think it's fair to put the blame on Mackie.
I think it's more a problem with the new showrunner being bad at their job. The show in season 2 didn't know what tone to go for or how to structure scene.
Other people took the role for short periods of the first season due to the whole premise of the show being body switching, and they were all competent at being Takeshi Kovach. If the second season had been as competently executed as the first season, the recast wouldn't have been a problem (but probably wouldn't have chosen Mackie unless it turned out the problem really was just the director making him act badly).