Why don’t scientists know that God sends prophets?
Because scientists do not know everything. Many do not even ask whether God exists, and someone who does not know God cannot recognise that He sends prophets.
The question rests on an assumption that is not true. Scientists know a great deal, but not everything. Each of them knows a small part of the world very well. About much outside their own field they know no more than anyone else.
Natural science studies what can be measured, weighed and repeated. It asks how things work. Whether there is a Creator behind everything, and whether He speaks to human beings, is something it cannot test with its instruments. That is not a weakness but its limit. The first verse above speaks of people who know the outward side of life well but are blind to what lies behind it.
Besides, many researchers do not believe in God at all. Someone who is not even sure that God exists will hardly recognise that God sends prophets. The question of prophets only arises once a person has found God.
There are also scientists, however, who believe in God and see His traces in the order of nature. So knowledge of nature and faith do not exclude each other. But a person does not find the way to God and His prophets in the laboratory alone. They find it with the heart as well, through honest reflection and prayer.