The laining is chosen (on many holidays) to deal with the holiday, itself. As the Rambam explains,
וקוראין בעניין המועד, לא בסדר השבת. ומשה רבנו תיקן להן לישראל, שיהיו קוראין בכל מועד, עניינו; ושואלין ודורשין בעניינו של יום, בכל מועד ומועד
On the first day of Sukkot, we read a lengthy passage which closes with the mention of Sukkot. Then (outside of Israel) on the second day, we read the same thing. On the 2 yom tov days of Pesach (beginning and end) and Shavu'ot, we read different things. And it isn't like we have nothing else to read that mentions Sukkot -- we could read from Devarim 16 which mentions it as well.
So why repeat the laining on Sukkot instead of reading from Devarim?