AFAIU, Because 1) strictly speaking car chases were much more frequent than one would believe based on television reporting. Most chases were short and didn't end up on the nightly news. Time, expense, and opportunity, as well as the benefits (catching some guy who, at least in theory, could be picked up later) are definite limitations. 2) How is the helicopter (10-15 minutes away or worse) supposed to find the car if they're not being followed and aren't driving conspicuously, especially at night? Relatedly, 3) the point of breaking off the chase is so the suspect stops driving dangerously themselves. Being chased by a helicopter, or even the expectation of being chased, potentially creates a similar situation the new policies are intended to avoid.

Note that the new policies are aimed at preventing chases and dangerous driving (or at least induced dangerous driving), not merely breaking away after a chase has begun. So, for example, in SF cops routinely break off the moment they believe the suspect knows they're being followed, whether or not the suspect is driving dangerously. And much to the dismay of citizens, it seems in many (most?) cases they don't even attempt to follow the car at all.