You’d think but sometime these things are left behind nothing but a single chain-link fence, some have a local security company do a periodic patrol every few hours so easy to get in and out in between, but yeah other have multiple cameras & permanently stationed guards

Would have to know more about the specifics of this site before making a judgement on the perpetrators, but the ghouls building data-centres love to cut corners so would be surprised if they did so on site security