Narrow margins.
It was a real shame because he rode so well (as did Evenepoel). These little mini disasters are very annoying.
Fortunately it was a low speed crash so hopefully there's no real damage.
There will be massive margins and cracks in the upcoming stages. I do not trust any of the big 4 to be invulnerable. The course is incredibly hard and each has a reason to crack. Pogacar's reckless racing style is already showing its adverse effects today.