I mean that's clearly a good thing. If you are actually suicidal then you need someone to intervene. But there is a large gulf between depressed and suicidal and those phone lines can help without outside assistance in those cases.
You might want to read up on how interactions between police and various groups in the US tend to go. Sending the cops after someone is always going to be dangerous and often harmful.
If the suicidal person is female, white and sitting in a nice house in the suburbs, they'll likely survive with just a slightly traumatizing experience.
If the suicidal person is male, black or has any appearance of being lower class, the police are likely to treat them as a threat, and they're more likely to be assaulted, arrested, harassed or killed than they are to receive helpful medical treatment.
If I'm ever in a near-suicidal state, I hope no one calls the cops on me, that's a worst nightmare situation.
