Because the likelihood of a police officer getting shot by a criminal is far higher. Not just in domestic violence situations, but also in everyday policing. An example: here in Germany even if you push hundreds of kg of cocaine you'll get six to eight years behind bars. Not worth shooting a police officer at a traffic stop over it.

In the US? Decades behind bars at least, life if you're in a "three strikes" jurisdiction - that's a massive incentive to shoot the cop and attempt to escape when you got nothing to lose anyway.