There are two reasons that I can see.
One is that different cultures, races, tribes etc., have different concerns, especially where survival is concerned. So for instance inter-racial marriages may be frowned up or even not tolerated where the country is small, a monoculture and especially where there are concerns about the continuation of its cultural identity. However these don't really affect basic morality.
The other is where inhumane people have gain control over religious organizations or politics. So for instance the Hindu priests insisted that women who were widowed had to be burnt alive. Even today they suffer a social death.
"In much of Indian society—across caste and religion—a widow is
often perceived by family members to be a burden and sexually threatening toward marriages. "
The ongoing tragedy of India’s widows - Women’s Media Center (womensmediacenter.com)
I highlighted the word "often". You will find that it is not the people in general that are against the widow. It is inhumane people, who spread fear in one form or another to cause others, especially people, who are ignorant or haven't thought the matter through well enough that are sucked in and thus may think and/or behave immorally.
