It isn't worth the danger of a visitor bringing in a disease on their feet, clothes or vehicle that could endanger all the breeders on the property.
H5N1 resulted in culling millions of chickens and turkeys in the Midwest and West last spring.
Right now 10 European countries and India are dealing with massive outbreaks of H5N8.
Large poultry operations require workers to change clothes and boots in a clean room before they come in contact with poultry.
They use one color indoors and another color outdoors so any employee can spot someone not in compliance.
Our chicken group has coop tours frequently. However, we have boot washes at each site and I don't let anyone on the property that has chickens or has visited a place with poultry. I make everyone else wear disposable plastic boots.