As with many games their are different departments who do different things and riot is no exception. People who work on maps are not going to be the same people who design champions.
As much as I would like to see magma chamber or even other maps be released there are a lot of issues that come with making a map, especially a map that can hold more people. Game is balanced for both teams / how long the game takes to finish / equal jungling opportunities / access to buffs / access to major objectives (like dragon and baron) / similar route design for potential ganking opportunities / again route design only this time for effective escape methods / with more people probably more nexus defense turrets, would these turrets be OP and hard to kill, to easy to kill, or just right to kill / and also the over all design, look, and feel of the map.
Same thing goes with features such as replays and observer mode. There is going to be bugs and also with patches every 2 weeks there needs to be a way so that these features will be stable week to week. In fact in the most recent update to observer mode it crashed people out of the game and nothing at all was changed about it just once the newest patch was added to the server, boom it kicked people out of the game every time it was used.
