Because I said so! ~wink~ Just kidding.
There is an interesting phenomena that happens when you count in your head rather than count out loud. I have been teaching for 25 years now and I have seen this certain phenomena happen 100% of the time with all my students. What is this phenomena?
Time after time, when I ask a student to play their assignment for me, I ask them if they practiced it counting out loud, and of course the answer is always “yes”. So, I let them play the song counting in their head, while listening to the irregular rhythm.
After they complete the song, I ask them to play it again, counting out loud and to my amazement… every time… they rhythm is perfect! Hmmmm. 25 years, and still teaching. Still happens.
Do I have an explanation? I have lots of theories, but I still call it a phenomena because it works 100% of the time. Counting out loud engages your brain into paying attention to the rhythm. Counting in your head puts rhythm in the back seat.
So, that’s why I strongly encourage counting out loud until the rhythm is learned.