为什么人们不使用序号进行图像存储？

I've been looking around and I've seen that, for example, instagram uses big strings for naming their images (instagram/p/BB-cCvtje4k, for example), and so does facebook. Is there any cons of naming the picture like thisuser/1, and the next picture thisuser/2 and so on? Or is it bad practice doing something like the following on my server side code?I've been looking around and I've seen that, fo