Good question. Because someone is making a conscious decision to enter into their home, likely to either steal from them or assault them. They're being put into that position by someone else. A police officer has discretion to charge or not, maybe they flip a coin and decide to lay charges. That's a lot of money home a home owner. Especially when a civil suit against the home invader probably won't cover the bills (and be additional money).
An alternative, though obviously unlikely, would be some kind of home invasion clause with someone's home insurance.