If the reason we light candles on Chanukah is as a commemoration for the fact that the lights of the menorah burned for 8 days on fuel that was only sufficient for 1, why don't we light our menorahs in the same way the menorah was lit in the beis hamikdash? Meaning, why don't we light all 8 (or, if we really wanted to emulate the way the menorah was lit, 7) candles each day of Chanukah?
An alternative approach.
The answer to this question could depend on the answer to the question of the Beit Yosef as to why we celebrate Chanukah for eight days if we are celebrating the miracle (Shabbat 21b) that oil that should have lasted for only one day lasted for eight. We should celebrate Chanukah for seven days, since only seven days of the burning of the oil were miraculous!
The following two reasons (text taken from) (and) of the Beit Yosef himself might lead us to say that we increase the number of lights each day to symbolise our increasing wonder at the repetition of the miracle rather than lighting all 8 lights every day.
This does not seem to work for the first answer of the Beit Yosef that:
A full analysis of all the answers to the Beit Yosef's question is obviously needed.
The purpose of lighting is to publicise the miracle and not as a commemoration (in the sense of re-enactment) of the miracle of the oil. See Rashi on מבחוץ. Shabbos 21b .
Beis Shammai and Beis Hillel give different reasons for why they light in decreasing and increasing numbers of lights respectively.
The reasons are B”S – the days that are to come or the bull offerings of Sukkos (which decrease) and B”H – the days that have gone or because we increase in holiness and not decrease.
The reason for the changing number is not related directly to the miracle of the oil.