I will try to explain it in a different way
Heavily embedded social customs - dowry in India, Pakistan, Africa, etc, forced marriages in some cultures, FMG, smoking, etc can be very hard to change as it is what those countries are used to that for centuries or decades
A law can be made to address it but it doesn't mean it won't find opposition with some parties and will take time to be adopted
Same in the US - this country was born with the principle of protecting yourself with guns, it is part of its Constitution.
Add political turmoil to the mix, economical interests, lobbyists and it is not as simple as "make a law to fix the shootings"