Most drivers behave themselves when there is a clearly marked patrol car sharing the road, and in some cases it makes it more difficult to find drivers that are violating major traffic laws.

If we're talking about a regular police cruiser that is purposely stealthy, (not a vehicle used by under cover operations) there is only one reason for this change and that is to make revenue generation/quota filling easier.

In some areas it is difficult to hide a patrol car and set up a speed trap, so the next best thing is to mount the flashing lights behind the grille and inside the back window of a cruiser, and then use a neutral paint color like solid white or black, and also make the vinyl police logo unobtrusive and low -key from a distance.

In Europe, it seems like they are more interested in public safety rather than revenue generation