Just played all 4 episodes a few days ago, and this was indeed the big question I had. I was wondering if the comics had an explanation, I haven’t read them (or watched the television series, so I should be careful around here
I did read a possible explanation on another forum.
It speculated something about the “zombie virus” being dormant, untill
you die, then it gets active, and you turn. The problem with a zombie bite would be, that a zombie already has an activated virus, and you’d get an active virus in your bloodstream because of the bite, so you’d turn while alive. Seemed plausible to me, but again, I’m no expert on the walking dead universe, or zombie virusses in general