The problem with standardized tests is that they tend to be very brief slices of time in a very limited format, with no documentation of actual work. They have the advantage of being, well, standardized, but that's also their weakness (think, for example, about the legal requirements that tests be adapted for medical conditions, and then generalize accordingly).
You might think actual work shouldn't matter, it's the endpoint, etc. but think about it this way: tests are subject to cheating problems, and randomness in scores. Let's say you have a choice of two surgeons: one who has passed a standardized written test, and one who has been certified by a panel of expert surgeons as reaching a certain level of proficiency by means of graduated practice exercises over the course of a year. Which would you prefer? This is an extreme contrived example, but it illustrates a broader point, which is the reason why traditional grades exist is because they reflect a long-term process and documentation of actual time in activity, which is important to learning.
You might think actual work shouldn't matter, it's the endpoint, etc. but think about it this way: tests are subject to cheating problems, and randomness in scores. Let's say you have a choice of two surgeons: one who has passed a standardized written test, and one who has been certified by a panel of expert surgeons as reaching a certain level of proficiency by means of graduated practice exercises over the course of a year. Which would you prefer? This is an extreme contrived example, but it illustrates a broader point, which is the reason why traditional grades exist is because they reflect a long-term process and documentation of actual time in activity, which is important to learning.