Because it takes the least amount of time and effort to get the answers you need. Most people want to do the "right thing" to catch the bad guy, and will help out a LEO without a warrant to that end.
Plus, who wants to sully a relationship with people who have the power to make your life and business miserable?
Sadly, I image you're correct. But you're speaking of regular citizens, not the law enforcement officers. The officers would seem to have a greaty duty than ordinary citizens, no?
What duty do they have other than to ensure they get credit for a job well done and to continue their career building?
They're people driven by the same selfish pressures most are, but there is little oversight or regulation to keep that in check.
Getting answers quickly and cheaply is considered good investigative work. A warrant is a last resort and exists as a check against their desire for answers from someone who is unwilling to comply.
I guess for all practical purposes, no other duty. I am 100% positive that all law officers take a special oath, and are also treated differently according to the letter of the law. Police officers are allowed to carry firearms and shoot people legally, after all. In addition to extra leniency about capping people, law officers have additional legal duties. I mean, we're treated to "ignorance of the law is no excuse", so I must believe that law officers aren't ignorant of the law, and have extra legal duties. So in practice I agree, they're motivated by all the same things the rest of us are, but we give police special privileges, supposedly in return for extra responsibilities. i believe we (including the law officers themselves) should hold law officers to higher standards.
Plus, who wants to sully a relationship with people who have the power to make your life and business miserable?