Flyingconsultant
a large flock of birds can be seen, and evasive action can be taken on the descent, although there is no predicting that the flock might not take the same evasive action and so still result in a bird strike.
On take off the attitude of the plane may be such (nose high) that the birds flying level are never seen. Furthermore the plane will likely be slow and heavy.
There are still such things as accidents. Not everything in the world is avoidable