The advancements in equipment to clean up after a large and/or complicated derailments contributes to these "acceptable" number of derailments. This includes roadbed, rail, and specialized equipment to move cars and locomotives. There are even 3rd party companies that specialize in railroad derailments.
Large wrecks can be cleaned up in 24 hours.
https://www.youtube.com/watch?v=qkui84o6rNA