The only thing I never understood about Japanese titles - especially if we're talking about smuts - is why they are longer than the transoceanic route from Europe to America and why they feel they need to explain in the title everything that's happening in the first 5 hours of the story. But maybe it's just me...
JP Competition culture and attractive requirement.
Long title = People interest why it's long = Stay long in people's mind.
Even getting people trying to abbreviate it into short name is part of keep in people's mind strategy.
Usually short title after you finish it, you'll hardly remember it unless it's unique and doesn't have dozens of similar products with similar names.
So to outstand from all of those, having long name and putting partially the plot in it are likely the current standard way for JP works to stand out or attract people at all.
Also another reason why adding plot or partially events into title, just to reduce the amount of people later refunding or giving up on certain products just due to they don't like the topic/game/anime/movie/whatever.
So if you know partially what is it related by its name, you'll less likely to watch it if you don't like it, so no mass refund later by those people at all.