It is probably because it took you a long time to file Citizenship. I remember my grandmother was asked way back by the IO, why it took her 20 yrs before she filed Citizenship.
N-400 - 5 Yr Residence
DO Norfolk VA
April 26 - Sent the N-400 Documents to Lewisville TX.
April 27 - Received and signed
April 27 - Priority Date
April 29 - Check Cashed/Posted in Bank. Deposited check April 28.
May 2 - Received NOA in the mail
May 3 - Email FP Notice Sent
May 6 - FP Letter received (May 31)
May 10 - FP Walk-in. ASC USCIS Norfolk, VA.
May 16 - Testing and Interview
Aug 31 - Interview Date
Oct 17 - Oath Norfolk Court House, Granby St.