They really can't. 1914 is the year that Jesus came in his invisible presence, was enthroned as King, and then began examining the churches to find his "Faithful Slave Class". 1914 is the very foundation for all of this. The Society has also used various numbers from the book of Daniel to count from 1914 to 1919 when they were chosen as the Faithful Slave. The Society would also have to radically change their Gentile Times doctrine; and separate it from the Seven Times of Daniel. Trying to abandon 1914 would create more problems that it would solve.
I think that it is so much easier for them to cling to 1914. It's easier to discredit the secular history than it is to deal with the headaches of having to reconstruct several other doctrines attached to this date. JWs have been effectively convinced that 1914 is the beginning of the end of the system of things due to WWI anyway. It's much easier for the WTS to simply discredit the secular sources and to continue to retain the claim that it is only the "apostates" who want to nit-pick over it. This method has worked quite well for many years. Why change it?