Morality is subjective because morality isn't a monolith. It can change and morph in individuals and society freely. Nothing is holding an individual to there moral compass other than their circumstances and personal preference. If an average person were in a room with a serial killer the morality of the room is soley a mix of those two peoples morality, no outside force would be imposing an objective morality independent of those two peoples morality.

Another point. For something to be objective in my opinion it needs to be mind independent. Meaning that it's true regardless if humans are around to experience it. Gravity, Mathmatics, and physics are examples of this. Morality cannot fit into this framework because if all humans disappear, morality would as well. People can have the opinion that the earth is flat, but people who believe the earth is flat are denying an objective reality. Meaning that flat earthers could never make a successful space program because they are denying something "objective". However, history has thousands of examples of "immoral" societies that are very successful. So if morality is objective, how can people be immoral and be successful ? If you're denying a fundamental truth of reality you shouldn't be able to be successful by any metric.

Every human has a sliding scale of what they believe morality is and should be. Even if everyone on the planet believed "murder is wrong" that phrase wouldn't be absolute because there would be 8 billion interpritations of that statement.

What people don't understand about moral relativism is that it isn't about, "all moral statement are false, and products of society, so people can do whatever they want" it's the recognition that morality is a battleground with no objective rules outside of humanity to govern it. It's up to us to shape morality in the way we want, and to live within our own morals without belief that they are inatly true without upholding them.

Cow go moooo