Why are people so quick to count out people at jobs?

At my new-ish job, ever since the first day I walked in most employees have rolled their eyes and acted like I’ve been there for 2 years. It seems to be like all the older employees mostly female that have been rude. The employees my age 20-23 have been very accepting and respectful. I’m a person that gives people Chance after chance after chance but am thinking about stopping since it feels like everytime a door is slammed in my face. Because of this I’ve brought headphones in order to block out their comments or faces they make so they don’t get me down or upset. Is this just a coincidence or does this type of thing happen at a lot of jobs?
Why are people so quick to count out people at jobs?
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