For me specifically it is because I have dyscalculia. Which made all mathematics is school quite difficult. I could understand reasonably complex ideas and through my own methods could solve equations but I couldn’t show my work because it was all done it my head.
It took me until grade 10 or so to come up with a method to know the multiplication table but it still takes more than a moment to work a simple calculation out.
Oddly I can work out and calculate the weight of a trailer of freight within a few hundred pounds with very little information in order to balance it for shipping but 9 x 8 involves 10 x 8 = 80 - 8 = 72
I failed math multiple times until I was put into math B for the slow people. I did better than the teachers assistant on tests. Went back to regular math the next year thinking I could do it if I was so good at remedial class and failed within a few weeks and stopped going.
When Gaza is nothing but corpses then the rest of the world will roll out the “There is nothing we could have done, we had no idea it was happening.”