I find the US border a pretty unpleasant place, and on paper I'm about as privileged as a person can be. On 3 occasions I've been detained for hours, had my phone seached through thoroughly, asked the same question 5 different ways in a manner clearly designed to try to catch me out, and generally been made to feel unwelcome. Admittedly this is 3 in probably 200+ entries, but there have been further minor instances, and I've travelled to other places as frequently and never been made to feel like that. I've never had my phone searched anywhere else, not even the UK.
So I can completely understand why someone might make decisions about which port they enter the US through. In my case I have chosen to stop entering through quiet ports where they a lot of time on their hands, as those have correlated with bad experiences, in my case I don't think preclearence would help as it would just cause me to risk missing my flight. But I can fully imagine why someone with different concerns around questionably-lawful detention might prefer preclearence ports.