Because he is not immune to reverse controls. Currently his "easter-egg" ability allows him to ignore 1 or 2 interaction with a champion and a node. Other than that, he does not have such ability
For now, not very much, as it is not stated anywhere in the game. It might get added to his abilities in the future to reflect the specific interactions where he can negate an ability, but for now is just hidden in the game
As others have pointed out, he has never been immune to reverse controls themselves. However, his helmet provides immunity to the reverse controls specifically triggered by Emma Frost's telepathy (a nod to the intention of the helmet, which is to block psychics from the mind of the wearer). Reverse controls from a node, however, are not psychic attacks from an opponent, and thus do not allow Magneto to bypass them.
As others have pointed out, he has never been immune to reverse controls themselves. However, his helmet provides immunity to the reverse controls specifically triggered by Emma Frost's telepathy (a nod to the intention of the helmet, which is to block psychics from the mind of the wearer). Reverse controls from a node, however, are not psychic attacks from an opponent, and thus do not allow Magneto to bypass them.
This is not quite right as I pointed out in another post about this same topic. Magneto is immune to reverse controls via a "psychic resistance", so he DOES work to bypass some reverse control nodes. One example is the Delirium node in 6.3.1 (and wherever else it may be) because it specifically states that robots and champs with psychic resistance are immune to it.
Some of the other reverse control nodes, including the one currently on the Magik boss in the EQ, do not grant an exemption for champs with "psychic resistance" like Delirium does, which I believe is the reason he is not immune to that node.
Comments
Currently his "easter-egg" ability allows him to ignore 1 or 2 interaction with a champion and a node. Other than that, he does not have such ability
It might get added to his abilities in the future to reflect the specific interactions where he can negate an ability, but for now is just hidden in the game
Some of the other reverse control nodes, including the one currently on the Magik boss in the EQ, do not grant an exemption for champs with "psychic resistance" like Delirium does, which I believe is the reason he is not immune to that node.