This kind of thing has always happened. There have always been a silent majority within societies that don't do anything either during an immediate crisis or a slower crisis, in almost every society. People often think "it's not my business to get involved" even when they are direct witnesses to things like child, spousal, elderly or animal abuse, or crimes happening. Sometimes it's fear for themselves. At other times what's being seen is so out of the normal for the person that their mind freezes and either tells them they're just not seeing it or they're frozen, unsure of what to do. And sometimes it's just plain old ""NMB Syndrome", or "not my business", and they just don't want to be bothered because it doesn't directly affect THEM (kind of like people who don't want others to receive benefits but when THEY need it, it's suddenly important).
This is at the heart of the German pastor Martin Niemoller's famous statement that "first they came for the Jews", etc., and what he spent the rest of his life and career after WWII trying to raise awareness about and prevent. Tons of social scientists have been occupied by this question and have done studies, and many have spent their whole careers specializing in it. It's nothing new at all.