Seriously, how did Yibum get into this thread?
Its connected to marriage since according to those (and its not the sages like you said) then Yibum would cause even more problems where the guy would have to divorce his first wife to marry her then (what if they are perfectly happy, etc.) Or this Mitzwah is annulled?
And you beat me to Dr. Dan's statement of "the sages forbid this". - It is not true. No sages of the Talmudh forbid this. Rabbeinu Gershom in Europe (thus only applied to Askenasim at a certain time, if at all) forbad it for unclear reasons and only for a certain time- the Yaabetz explained because of the jealousy of the non-Jews of Europe who would have an extra excuse to persecute Jews.
The Sefardim never took this upon themselves. Only because of laws of other nations (like the U.S.) and the state of Israel (which secular laws don't really apply to Jews anyway) was/is this not done.
Even the Askenasim today are in no way bound by the decree, which expired a long time ago, + even those who were strict said perhaps 1,000 years. Guess what, the 1,000 years were up in the 1,900's (forgot the exact date).
If people personally do not want to, that is their problem, all I am trying to do is to clarify
what the law actually is without the usual biases that we get today -like "it's not preferable by the sages" and other such statements, which some men (usually because they are afraid of the whip of their wives or because of the western culture and though patters permeating their thoughts.