Because of this saying of Allah Almighty: "So let them not approach al-Masjid al-Haram after this year of theirs." [Surah al-Tawbah: 28]
And this is also the view of Sa'id bin al-Musayyib (may Allah have mercy on him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / Q4330