Why are people afraid of change?

For the most part, people are afraid of change. They understand that change is necessary, but they'd much rather such change to take place gradually over time. The villagers in "The Lottery" are also highly resistant to change, opting instead to hold fast to the old traditions. These traditions endow the villagers' lives with meaning, order, and stability. They provide some degree of certainty in an uncertain world. But the problem here is that the villagers follow tradition blindly, without questioning its basis, or asking themselves whether it should even be allowed to continue. Even when one of the village's most enduring traditions involves human sacrifice, the villagers still stubbornly cling to the old ways.
To some extent, this is a product of ignorance as much as anything else. The villagers have never known anything but the old traditions; their lives are virtually meaningless without them. There's also an element of fear involved. Some of the older generation in the village genuinely believe that their whole civilization will collapse if they follow the example of other villages and cancel the lottery tradition.
Ironically, the villagers have come to link the moral health of the village with the very immoral tradition of the lottery. In sacrificing an individual, they believe that they're ensuring the village's continued survival. Tradition, even if it involves an act of barbarism, is the glue that holds this society together. Without it, no one knows what might happen. It's this uncertainty, combined with fear and ignorance, that motivates the villagers to carry on with the old ways of doing things.