Sincerity is probably right.
There are other reasons, they may have OCPD traits where they are obsessed with detail so they have to tell you everything. My father did this.
Or he may just be a beater around the busher :)
Why does my husband repeat his "entire story" during a conversation, before I can give a response?
Do you mean he is wordy? Is he out of work? Many people who are isolated / not working every day and have lost that sense of how much to say & how much not to say and they tend to rattle on. Also, you don't mention his age, but many older people tend to grow wordy and not aware that brevity is usually the best route.