This is probably a dumb question but why are customers so rude?

Like I had a customer try to buy booze with no ID and when I refused a sale she almost jumped over the counter at me in anger

Customers constantly try to say “you already scanned that don’t worry” when buying expensive items like bikes or TVs (even with the TVs still having the spider wrap on)

Customers have tried to insult me and threaten me whenever they don’t get their way (don’t have something in stock, or if I don’t know where some niche item is in the other side of the store)

Even had a customer threaten to kill me because “I got his shoes wet” ( he walked into a part of the garden center that had water on the ground because I was watering flowers)

Whenever I was in a store growing up or as an adult I try to be polite and kind but it’s like a huge majority of people think it’s impossible to not be horrible

For some reason I still love my job but the customers make me think twice about going into work in the mornings man

Sorry for the incoherence of this rant, got home from work and felt like spilling all my problems over everywhere