Oh, they have . . . maybe not directly, but they know what kind of nasty chemicals are in there
When my husband was in high school, he very briefly had a job that involved digging around existing poles so they could get a fresh coat of creosote applied at ground surface level, which is where most of the damage gets done. Just because you never saw anyone doing it, doesn't mean it wasn't done. The same is true for railroad ties - they do get retreated.
Even without the issue of the cancer risk, creosote is nasty stuff. Shortly after my husband and I got married, he worked for a nursery that did landscape installations, which sometimes included using old railroad ties. One day, he had to use a chainsaw to cut some ties to fit a certain space. The saw, of course, threw chips all over him, and some got stuck in his socks. He didn't think anything of it, just went on working, and by that evening, he had some really nasty chemical burns on his ankles. It was bad enough, he was unable to wear his boots until the swelling went down. Not something you want to have contact with.