I’ve read this book a couple times and it was pretty good. Anyway, to answer your question. Mr. Jones neighbours originally thought they would over take the animals but when they noticed they couldn’t, they were worried about the farm overtaking other farms, which they did.
To answer questions like this one, think about WW2 as the book was based on that. You’ll notice small things in the book that indicate how similar WW2 and Animal Farm are related.