Why are some garter snakes seeking human habitation and how and why are they surviving without a pond of water?

Recently in the summer months every year, we are constantly seeing large garter snakes (I was lucky enough to see a baby one some time earlier this year or maybe last) in are apartment and what i'm trying to figure out is, is why are there many garter snakes living around in civilization, we'll see birds, raccoons, feral cats, and squirrels including some insects and the garter snakes here in the apartment but why are they living so closely here around humans? yesterday me and my (girl) friend were going to go outside to try and catch one or some but then at first no luck and then our friend had came because his metro phone got locked and he wanted us to go to the metro store so he can see what's wrong with it and so I put the container I had that I was going to put the snake in back in the house and as soon as we were leaving guess what? yup it was a large garter snake probably female? but the thing is it was me, my two friends, my little sister, and my (girl) friends daughter and we all saw it but why didn't the snake slither away, we were all very close to it especially me trying to get a look at it and it didn't even try to get away it just kept on moving like we weren't even there but why? and by the way I didn't catch the snake because I didn't have the container and plus we were inna rush anyway but I was glad I got to see a "wild" garter snake up close but why are these snakes living in human habitation especially in apartments because there are no rats, mice, fish, especially water unless it's raining or the sprinklers are on but there are some small species of birds and squirrels and a lot of species of insects so do you think that the snakes maybe eating those but what about water? there's not a single pond in my apartment? but how and why are these snakes surviving and what might they be eating and why are they living approximately so close to us humans?