What would cause the main bearing in a 2001 chevy s-10 with 87,000 miles to go out.

what would cause the main bearing in a 2001 chevy s-10 with 87,000 miles to go out.
It could be due to insufficiant oil reaching the main bearing, whether due to poor oil pump pressure or sludge build up preventing free flow. A low oil level can cause all kinds of problems to show up, but likely that bearing was the weakest link on the engine and that is why it failed before anything else.