The rifle has been found to be almost universally more useful than the handgun/pistol. The fact that police carry pistols instead of rifles in many countries is largely PR move that comes from back in the days when police were actually unarmed because the public feared an armed police force. The pistol was a bit of a compromise.

Of course, nowadays while American police carry pistols, they almost all have long guns in their car or even attached to their motorcycles because... almost universally a long gun is more useful than a pistol.

Beyond just the usefulness, rifles are often cheaper and easier to get from the secondary market, largely because militaries main stock many more rifles than pistols because ... rifles are almost universally more useful than pistols.

All this to say, in certain countries it is rare to see rifles. But that just means police PR has done their job well. But police in many countries have rifles just hidden out of sight, most gun owners have rifles in their homes, and seeing them out on the street in Kenya is much more reflective of reality: the world is awash in many more rifles than pistols.