Because they want to keep it longer.
There is a sh9oe for every foot.
I like First Majestic. They deal in bulk:
50oz. Poured Silver Bar
https://store.firstmajestic.com/collections/silver-ingots-and-bars/products/50oz-poured-silver-bar
The main problem I have with larger bars is that they are generally not as useful as a medium of exchange unless you are buying big-ticket items. 10-oz is really as far as I’m willing to go. If I want higher values, gold makes more sense IMO. I