Why don't cops conduct more non-custodial interrogations, as they do not have to read suspect miranda rights?

No arrest....

Nothing personal but you have never worked Law enforcement Have you? I doesn't work that way. May be once in a Blue Moon it could work. Crooks are much smarter than you think very few incriminate themselves. Police work has a lot of investigations and a Murder can skip without being read his Miranda rights. So why don't you just apply for a job on the force then try your own method of interrogation.

Non custodial interrogations (interview) are used to gather information. That information can be used to later charge the interviewee with the crime if other evidence shows that they were guilty. There is actually no requirement for their rights to be read because they are not under arrest. The difference between the two is that in an interview, one can get up and walk out at any time. Custodial interviewee don't have that option as they are under arrest.

Because sometimes they can't risk the suspect leaving.

Let them take more of our rights away. Yea that's the way to go.

Because they could just walk away. Hey did you murder him? No, f you. Peace.