I found some cheap flights from London to Tokyo on Google Flights that I plan to buy. However, the flight has a stopover: the legs are London to Moscow, then Moscow to Tokyo.
I thought that, instead of spending 4 hours at a Moscow airport, maybe I could try to buy my flights separately to allow me to spend a whole day in Moscow, and I will spend a night exploring the city. However, when I search on the same dates Moscow to Tokyo, I find that this stage of the flight itself is much more expensive than buying the combined flight from London to Tokyo. Is there any reason for this? Is there any convenient way to find flights that extend the stops on purpose for a day or so?