Because of this saying of Allah, exalted be His praise: "And remember Allah during a few numbered days." [Surah al-Baqarah: 203]
So Allah Almighty kept it general and did not restrict it, and He said: "Then when you have completed your rites of Hajj, remember Allah as you remember your forefathers, or with even greater remembrance." [Surah al-Baqarah: 200]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / Q6283