There can be many reasons as in she is working back in home country or something.Its not that people do not do it.My friend got PR without spouse and when asked he honestly mentioned the reason that he doesn't want to relocate his whole family without being sure of his financial condition in the new country and this was accepted.Besides, bottom line is always the funds and CIC makes sure that a person who is married shows enough POF even if the spouse is non-accompanying so dropping spouse just to get ITA is not something illegal or wrong.but if he chooses to drop her now from her application I think he has to provide a legitimate reason for her not accompanying.
what reason he can give?
asking coz I am also in the same boat.