As people search in Historical Images they see things they are interested in and wish they were indexed. Why not let them offer to do so. They would be motivated to work on those records of interest.
Unfortunately, it's not that simple. FamilySearch generally doesn't own the records, and getting them indexed involves complex contracts with the actual record owners/custodians. Once a contract is hammered out, the indexing project has to be set up, answering all sorts of complex questions about what fields need to be included and what types of data should go in those fields, how many images to include in a batch, how many entries an image should default to, and so forth and so on. At some point, the metadata (the parts of the index that many entries have in common, such as the collection title or the location of the events) needs to be set up, which is a highly non-trivial task. And throughout the indexing, someone needs to keep track of what's done and what isn't.
Obviously I had no idea how complicated it was. Thank you for taking the time to inform me.
It is even more complicated than that. Cataloging has two main parts: imaging and indexing. Before any imaging can happen, there must be an agreement in place between FamilySearch and the record custodian. Some batches were imaged decades ago onto microfilm, before anyone dreamed of the web. So, many of those agreements need to be reworked. Only after an agreement is in place that allows indexing can indexing begin. An agreement allowing indexing may not allow viewing of the page image by anyone other than the batch indexer.
Indexing used to be done by people. Now it is being done by machine, with review and correction by people. The review and correction process helps to further train the machine.