The reason we do not wear Tfilling all day is because one Friday a man was travelling and shabbos was coming and he saw a man wearing Teffillin and figured he was an honest jew and gave him his money
After Shabbos the man went back to the Tefillin man asking for his money , The Teffillin man denied ever getting the money and the original man went to the Rav telling him what happend (Sorry I forgot which rov this was) and the Rav figured out the man who was wearing teffillin was a theif and did have the money
they then ruled that people should not wear Teffillin all day