It's a metaphor for unheeded advice or unfulfilled demands, just like a puff of wind passing through the ear, without leaving any trace.

Ex.: My words are taken as a puff of wind in my son's ears, while what his teacher says is decree.

If people say you have "soft ears", they mean you are easily persuaded, credulous, or susceptible to flattery and provocation.

Ex.: Lao Zhang is a very nice man, but has "soft ears", believing in whatever he is told he never has his own definite opinions.