＞I can't speak for the popularity of Mortal Kombat, as I know very little of the fighting games scene. So I will stick to answering your other questions.
＞American media aren't often made into animes for a variety of reasons. The biggest of which is indeed probably the fact that the source material is often unknown or unpopular. That being said, many American TV shows are often more known than one might expect. Prison Break and 24 were massively popular. South Park is gaining prominence. And many people look back fondly with nostalgia at Full House. For these kinds of shows though, there really isn't any "need" to make them into anime. Animes are often adapted from manga or light novels, both of which are "still" mediums, and rely in part on the reader's imagination for depicting scenes. TV shows on the other hand don't need to be animated, as they already fully depict the scenes.
＞Bethesda's games are indeed quite popular. As are games like Minecraft, Terraria, etc. There are also many Japanese gamers using Steam.
I will just answer to your question coz I don't know how popular Mortal Combat is; I don't know so much about what's going on in the fighting action games.
One thing I'm sure is that they hardly make amine from those [media? NOT SURE AMBIGUOUS -5point] in the United States for various reasons.
The biggest reason I assume is the lack of popularily of the contents.
Compared with that, TV shows are much well known to the public more than you expect. Prison Break and 24 are the good examples of which are very popular. South Park is getting more famous.
And, Full House has many fans who enjoy the time back in the year it was released.
I don' t see any reasons why they need to make anime out of these programs.
I think animes are made out of contents which often need readers to fill and strengthen the worlds with their imaginations.
Since characters and scenes aren't static in TV programs, these kinds don't need people's hands to get animated.
Games by Bethesda are popular here, as much as Minecraft, Terraria, and etc. Many of the Japanese gamers are using Steam.
