Because an automated screening system allows the company to screen many more candidates without interacting with them, which they will do, which will make the majority of these screenings wasted effort.

Let's look at two cases to see why this is: Case 1: company does 10 30 minute in-person technical interviews for a role for equally qualified candidates, doesn't use automated testing. Every candidate knows that because they're talking to a human, so they know they're dealing with a human hiring process that deals with time constraints. They KNOW that they're one of a small group of people selected to move forward. They can reasonably calculate a value for their in-person technical interview as having a 10% chance of success. If they do 7 interviews like this they have a >50% chance of getting hired by someone, which would take them only 3.5 hours of interview time to achieve. Each such hiring process has only take up a combined 5 hours of candidate time.

Contrast this with case 2: company uses your system, and so technically screens 1000 equally qualified candidates in the same period with no human interaction. The candidate now has no idea where they stand in the applicant pool, but they effectively have a 0.1% of getting hired by this company. If they do 666 interviews, they still don't have a 50% chance of getting hired by any company doing interviews like this, and they will have spent two whole weeks of their life not eating or sleeping, just doing interviews. That company will have wasted three weeks of candidate time conducting this round of interviews.

Furthermore, the 10 minute time difference is irrelevant, the candidate already doesn't care when they do the interview, and the pressure in no way lessened. They still have to perform in a 30 minute window, and they will still be nervous. The only difference is the recorded screening is more impersonal, which allows the candidate less opportunity to make a human impression on the hirer.

Your system assumes the applicant's time has no value.