Easy barriers provide valuable information when not passed.
Valuable, trustworthy information about others can be challenging to come by given the vast amounts of low-value information many boast about. It is difficult to sort out the legitimate claims to fame from those that proudly wear fool's gold, making those that are actually valuable get sucked into the noise that is society.
Information can be given not only in a positive manner, but a negative one, e.g., this action was not performed or credential not attained. Setting low barriers to entry earlier in the filtering process allows time and effort to be saved in the long-term by eliminating candidates that are probably (or in some instances, obviously) not qualified. While some otherwise-qualified candidates may be culled from the herd, there are often others of similar quality that do pass the initial filtering.
At a certain point the information offers diminishing returns, and it is at this point that the bar should be set: any lower and the unqualified may get by, any higher and nothing extra is gained.
Exceptions exist for all of the following examples, but they are exactly that: exceptions.
Graduating high school is low effort and requires a modicum of discipline and pinch of motivation. Just show up, do some homework, take the exams, and at least attempt to pay attention during class. The teachers nor administration nor school district want you to fail.
The bar to many "career" jobs should be set at having graduated high school. If the candidate didn't graduate, they are probably lacking in a few departments that constitute a good employee.
Maintaining a good credit score is simple, but not necessarily easy: ensure the credit card balance is always less than the bank account balance minus any future expenses. Spending money that doesn't exist yet, and may not exist due to a variety of reasons, shows short-sightedness and poor decision-making abilities.
The bar to many financially-related endeavors is rightly so a not-bad credit score. (There are arguable issues to this, such as people who choose not to have a credit card being lumped into the bad credit category. But if someone is good with money, then they should just play the game since it won't hurt them.)
Achieving a 3.0 GPA, or an average of a B (80-89) across all courses, can be challenging to achieve for some, but is still within reach with the right amount of effort. There are tutors, both private and included in tuition; professor and teaching assistant office hours, which can often get you pity points when it comes down to the end; hundreds of hours of online content for free on YouTube; textbooks available for pirating with hundreds of example problems and solutions; smart classmates who need friends or desperately want to show off their smarts. Achieving a good GPA, whatever that value may be (but it's quite a bit above a 3.0), shows both intelligence and discipline, two desirable traits for employers.
Many reputable companies have a minimum GPA requirement between 3.0 and 3.5 to immediately bar what they consider low-quality candidates from applying. I suspect this works well and will assert two statements:
Choose bars that are easy to pass and directly test for important candidate characteristics (e.g., discipline, lack of impulsiveness, etc).
Make sure the bars don't entirely rely on external factors outside of the candidate's control, or if it absolutely has to, allow for an explanation to be made as needed (e.g., "my credit score is low because X" can be a valid excuse that may bar some candidates).