In Biblical point of view:
1) Everything was good at the beginning.
2) God was rejected and degeneration begun.
3) In earlier time there was not as much mutations, gene pool was "perfect", without errors.
4) At the flood time situation was still relatively good, much better than now.
5) After the flood, DNA are has continued to get weaker, more and more errors in copying. And more other changes also, for example from one bear couple, all modern bears.
That is why you can't see any bottleneck. There simply is no good reason why there should really be one.