The correct answer is - Catholic missionaries.
When the Europeans came to the territory that was once occupied by the Maya civilization, they brought their religion with them as well. One of the reasons they brought Catholic Christian missionaries was to try and convert the native population, thus controlling them easier and making a more unified environment. As it happened more often than not, the missionaries undertook extreme measures, and they gave their best to destroy pretty much everything that was related to the Mayan religion, and just 4 pieces of the bark-paper documents, better known as the Mayan codices, remained to witness for their time.