I can't provide a citation but my memory matches
@Charlaquin's on this point. I want to say that one of the designers made this claim in an interview or promotional article at about the time
Xanathar's came out. Essentially they chose to go with names for books in 5e that were not repeats of books from earlier editions (so no
Draconomicon or
Manual of the Planes), or previous titles with a number (so no
Player's Handbook 2), because their market research indicated that those titles created some confusion in at least a portion of their target audience.