In Talmudic times, it was common for one to wear tefillin all day long. As the Torah does not limit its observance in any way, there would seem to be no reason to limit time spent wearing them to a few minutes a day. Even the exemption from wearing tefillin at night and on Shabbat is subject to much Talmudic dispute, with many asserting that Shabbat z’man tefillin hu (“Shabbat is a time for [the wearing] of tefillin”).
The Talmud teaches that everything is dependent on mazal, “even the Sefer Torah in the ark”. Some sifrei Torah are used week in and week out, while others only see the light of day on Simchat Torah. So, too, certain mitzvoth “get lucky” and are widely observed, whereas others are somehow neglected. And mitzvoth that enjoy widespread observance in one generation may be less fortunate in another.
Human nature is to be forgetful, even in the midst of doing something. This human frailty is what leads the Mishnah (11a) to rule that a tailor may not go into the street with his needle nor may a scribe go out with his quill on Friday afternoons just before dark, lest they forget and accidentally carry their materials on Shabbat (in a place which has no eruv). Yet, the Gemarah (12a) rules that one may go out while wearing tefillin late on Friday afternoon, as “Rava bar Rav Hunah taught that one is obligated to feel his tefillin every moment and moment”.