In previous generations, it was the custom to wear Tefillin throughout the day. Even after Davening, Tefillin was worn when going about one's business, in the street and at home. However, in later generations, Yidden had lost a certain degree of commitment to the Mitzvah of Tefillin (along with other Mitzvos).
Rebbi Shimon Ben Elazar said: Mitzvos for which the Jews gave up their lives - in the time of a government decree - are still upheld with a strong commitment by the Yidden, such as: Bris Milah and not serving idols. And all those Mitzvos for which the Yidden did not give up their lives, still lacks commitment and is "weak" by them... such as Tefillin, which is still "weak" by the Yidden. (Shabbos, 130a)
Have you ever been on a highway and saw flashing blue and red lights up ahead?
If you're like most drivers, your first instinct is to hit the breaks and slow down. As you near the source of the lights, your speed slows to exactly within one MPH of the speed limit, as does the speed of the other cars sharing the road at that stretch of the highway.
Then, as the glaring lights fade into dots in the rear-view mirror, your speed climbs back to the (hopefully safe) number it was before encountering the lights in the first place.
As technology evolved, a driver may receive a prompt "police reported ahead", soliciting a break in speed, even before seeing the police, albeit not as drastic as when seeing the lights, but significant nevertheless.
According to many opinions, the question about reclining is only asked at the Seder nowadays; it was not asked during the time of the Beis Hamikdosh. This is because the prevailing custom in those days was to recline during all meals, not only on the night of Pesach.
As such, reclining on the eve of Pesach was not an anomaly; it was as normal and "ordinary" as making Kiddush - something the child was accustomed to seeing. And, since reclining on the night of Pesach was considered usual conduct in his family - something the child took for granted - seeing his family recline did not pique his interest; it did not seem out of place. Hence, it did not beget a question.
This is just what we do.
In previous generations, it was the custom to wear Tefillin throughout the day. Even after Davening, Tefillin was worn when going about one's business, in the street and at home. However, in later generations, Yidden had lost a certain degree of commitment to the Mitzvah of Tefillin (along with other Mitzvos). 
