You watch too much TV. Its hard to have dialog in the show unless there are partners.
Seriously, the only places you see two officer cars are in areas where crime is so rampant that cops are afraid to go alone.car.
Around here, it's because cops prefer to cruise with a buddy (wouldn't you?), and have a union that's strong enough to call the shots. And, of course, because we have a chief and city council who are too spineless to press the issue (you just know the union's PR response would be "they're needlessly endangering our brave boys in blue").
The FBI collected information for a period from January 1960 to September 1962 and found that in American cities deploying both types of vehicles, 65% of the officers killed while on duty killed were in two-officer vehicles while only 35% were in one-officer vehicles. This statistic seems to indicate that the presence of a second officer does not guarantee personal safety.
No. And they are less likely to kill innocent bystanders or other people who aren't actually a serious threat, too. Maybe when they're alone, they're less likely to be asshats, and not be playing to their buddies. Maybe it's "mob psychology" that affects the cops. (And of course, maybe it's that if they're alone, they won't go anywhere that might be dangerous until backup arrives.)
And it's not as if cop is that dangerous a job. Being a garbage man, farmer, or truck driver is far more dangerous (top 10 US dangerous occupations: fisherman, logger, pilot, garbage collector, roofer, structural iron worker, farmer, truck driver, powerline worker, taxi driver). But we don't have any TV series about garbage collectors.