In a bunch sprint you want and need to be focused 100% on what’s happening around you. Not just for your own race chances (which as you say are pretty meaningless in the context of an amateur race where the podium spots are already gone) but for the safety of yourself and everybody around you. Slowing down or looking around to check on the status of crash victims is extremely dangerous when you’re moving at high speed in close proximity to other riders. Crashes at that point in the race are common enough that you just tune them out until you get to the finish and it’s safe to find out what’s happened and offer help if needed. That last 500m is going to be done and dusted in ~30 seconds. And there are going to be a lot of people near the finish who are much better equipped to help an injured rider than another racer - race staff, medical support, spectators who are cool, calm and collected rather than running around in cleats with their HR at >90% max. If it was a rider who fell on a descent in the middle of nowhere with no spectators or race support around and only other riders to help, that would be a totally different scenario.
Whenever I’ve seen riders crash in less intense parts of the race, people have always checked they’re OK and stopped if it’s clear they need help and there’s no other support around. For a bunch sprint crash it’s also much easier and safer for the following racers to check and stop if necessary, than for the people who are in the middle of the sprint. People who have been dropped, already done their work positioning a team-mate for the sprint, or who simply don’t want to risk life and limb sprinting for 4th spot. The crash happened ahead of them so it’s easier for them to assess the situation, and they’ll be moving more slowly and spaced out so it’s much safer for them to stop if help is needed.
Cyclists aren’t an uncaring bunch, if anything the opposite, people look out for each other more than in many walks of life.