Backpain and the left leg-right arm movement pattern

In a youtube video named "Layne Norton's Lifting Instruction from Stuart McGill & Brian Carroll - PART 3" link we can at 7 minutes
in see how Layne Norton struggles to perform the simple bird dog bodyweight exercise.

In a youtube video named "Fixing Dave Tate: Lower Body Full Workout" link we can at 7 minutes in see how Dave Tate also struggles to perform this excercise.

Given that both Norton and Tate can squat and deadlift more than 3 times their own bodyweight they should have plenty of "core" strength.
So what is going on here?
And if training the diagonal (left leg right arm and vice versa) movement pattern is part of the solution (both Norton and Tate are experiencing backpain it seems)
could it not be an idea to apply this occasionally before the problem occurs?

Sorry Andy, there is too much information to unpack here and to answer completely is outside the time scope I want to spend on this forum. In short, McGill and the functional guy are viewing the world through a different lens than I am. The reason why they struggle to perform specific exercises is that the performance bottleneck is not strength. It is motor control. In other words, the exercise represents a new skill that has a balance/coordination component to it that they need to learn before being able to perform them well. It is very unlikely that the low load diagonal movement pattern is helping any more than any other low load general movement exercise perceived to be beneficial by the patient. The two best things you can do to help prevent future injuries is to continuing training and getting enough sleep. There is no evidence that these types of exercises move the needle in providing a specific benefit.

To piggyback off what Dr. D’Agostino said, there are countless highly specific movement patterns used in Physical Therapy, Chiropractic, and any of the legion of “functional movement gurus” that anyone, no matter their level of fitness or strength, are not going to be able to perform properly until they train that movement specifically. We actually count on everyone’s inability to perform them correctly because we can then convince you that you have a problem, convince you that we know the solution, and convince you that you need our services lest you be relegated to the end stages of movement “dysfunction”.