(I am a cardiologist)
This is an interesting thing, and needs to be followed closely.
There are a group of medications that have been made the standard of care for the treatment of a heart attack. These medications were tested in numerous high quality trials (randomized, double blind, placebo-control). But many of the trials are old. They don't take modern practices into account.
The problem with "just repeat the trials" is that trials are both hard and expensive. Expensive to get enough people enrolled in them and followed for a long enough time to get a good outcome. Hard because it's hard to enroll someone who is in the acute phase of a heart attack into a trial. Doubly hard if you are trying to test something that was previously believed to be the standard of care.
Imagine being a patient and being offered "We have this medication that we want to test whether it's going to help you after your heart attack. Would you be willing to be in a trial, where you are not sure if you are going to get the medication or not? If you don't want to be in the trial, you will almost definitely get the medication, because it's considered a lifesaving medication after a heart attack."
These trials are great and I give props to the study authors and their team to tease out this information. It's not practice-changing... yet, but certainly challenges the idea that every patient needs a beta blocker post-myocardial infarction (heart attack).
In reality, we are pushing more ACE-I than beta blockers on the discharge medications, but beta blockers are still on the list of required medications at the time of discharge to meet "quality of care" metrics. Maybe those metrics will get updated to be based on post-MI ejection fraction.