1.) Traffic stops and accidents.
2.) "Public order" issues (protests, large events, etc)
3.) As victims or perpetrators of a violent crime.
Most of us won't be either side of the equation in #3, virtually all of us will experience #1, and a large proportion will experience #2.
It's also possible that some of us understand that while many good LEO's exist, the bad ones are too damned dangerous and protected by the silence of the good ones. There are also competence, "War on Drugs" and other issues.
edit: Also, just ask literally any attorney what you should say, including those who have nothing at all to do with criminal defense. Then ask them why they all give the same answer as my original post...
An attorney is going to tell you what's 100% in your legal interests, since that's their duty. There's always a chance that you say something that incriminates you or reveals that you committed some other crime or similar.
But that's not the only consideration. There's also concern for the well-being of your community, a desire to make it safe for your children, etc. Acting on those interests can supersede the tiny risk that a law abiding citizen takes when speaking to law enforcement.
Remember, the person I responded to was talking about a home robbery, and so was I. Obviously you have to use your own judgement, and if it's the local PD asking about a missing person or a domestic incident, etc, don't be a dick.
The FBI agents then told me they'd be calling the DA to press charges and have me arrested for lying to a federal agent unless I completely cooperated with them in an investigation and offered them full access to my phones, my home and all my computers.
It is very likely in your best interest to avoid speaking with law enforcement.
The problem is more to do with the "average", and the system as a whole. We have a prison industry, terrible public defense, increasingly permissive treatment of fairly shady information gathering, and increasing militarization in urban areas.
The other issue is that Officer Friendly might not shake you down, beat you up, or screw you over. He might shut up and look the other way when Officer Hairy F. Knuckle does though. Blue Wall and all. That's hard to prove or even discuss, but it's painfully real.
But most of us, the overwhelming majority of the time, want to see law enforcement succeed and have nothing to conceal. If there's a robbery next door, I'm going to very happily tell the cops absolutely everything I saw and heard.
Edit: I'm surprised that this post is unpopular. Do you really want to live in a world where people don't help law enforcement find violent criminals?