Sai devotees - why Original Sai mantra OM Sai namoh namah ...... is reduced to Om Sai , Sri Sai Jai Jai Sai?

Both forms of mantra are same. It all depends upon the mental state and feelings of the devotee. For daily doing japa shorter form is preferred. Mantra sastra has definite guidelines on this. Single syllable "OM" is supposed to be more powerful of all the mantras. Intense love towards the God is more important than any mantra