Actually I think the cry for games to become MMO by some fans is because of the general perception that MMO are "better" then single player games. But before I go any further let me define what I mean by "better". Because they are multiplayer people can play them with their friends which is a common thread in gaming these days because despite what uninformed parents think most gaming is a "social" activity.
Next in terms of "better" is the longevity of the games. Unlike most single player games which seem to be getting shorter and shorter, personally I'm getting tired of buying games and beating them in a single night so I stopped buying and started renting. MMO often have massive amounts of game play that takes several months to go through all the content. While most single player games you can easily finish in under a week as a casual player. I remember one developer almost bragging their game has 10-12 hours of gameplay and I thought that's a single weekend worth of gaming.
Also I suppose it could be a third thing but it's tied to longevity in that most MMO get constant support and have updates and new content on a semi regular basis. This means a steady stream of new material and not having to wait years hoping a squeal comes out so you can get new content/gameplay in your favorite franchise.
But overall I think it is these two main things, the ability to play with others and larger amount of content, that make players call for a MMO of their favorite franchise. The problem though is not a lot of games are well suited for the MMO format. Like of the two you mentioned above I think Link would make a horrible MMO because it's always been heavily story driven and focused around you as link so it wouldn't really work since MMO tend to have a fairly static stories the players don't truly effect. On the other hand I think Pokemon would probably be a hugely successful MMO if done correctly. People would capture, trade, and battle their pokemon as well as have huge tournaments. As I recall the DS already uses it's Wifi to connect online so players can trade/battle their pokemon over the web so a MMO only seems like the next logical step for that so people can't cheat like they can with DS hacks.
Next in terms of "better" is the longevity of the games. Unlike most single player games which seem to be getting shorter and shorter, personally I'm getting tired of buying games and beating them in a single night so I stopped buying and started renting. MMO often have massive amounts of game play that takes several months to go through all the content. While most single player games you can easily finish in under a week as a casual player. I remember one developer almost bragging their game has 10-12 hours of gameplay and I thought that's a single weekend worth of gaming.
Also I suppose it could be a third thing but it's tied to longevity in that most MMO get constant support and have updates and new content on a semi regular basis. This means a steady stream of new material and not having to wait years hoping a squeal comes out so you can get new content/gameplay in your favorite franchise.
But overall I think it is these two main things, the ability to play with others and larger amount of content, that make players call for a MMO of their favorite franchise. The problem though is not a lot of games are well suited for the MMO format. Like of the two you mentioned above I think Link would make a horrible MMO because it's always been heavily story driven and focused around you as link so it wouldn't really work since MMO tend to have a fairly static stories the players don't truly effect. On the other hand I think Pokemon would probably be a hugely successful MMO if done correctly. People would capture, trade, and battle their pokemon as well as have huge tournaments. As I recall the DS already uses it's Wifi to connect online so players can trade/battle their pokemon over the web so a MMO only seems like the next logical step for that so people can't cheat like they can with DS hacks.