If not seven so how many times?
I'm not sure the actual reason, but muslim are guided by Holy Qur'an and Sunnah (al-Hadith), therefore I quote below hadith for referrence:
Sahih Bukhari: No. 1532, Narrated by Ibn Umar (may Allah be pleased with him):
The Prophet (may Allah blessings and peace be upon him) reached Mecca, circumambulated the Kaba seven times and then offered a two Rakat prayer behind Maqam ibrahim. Then he went towards the Safa. Allah has said, "Verily, in Allah's Apostle you have a good example."
Sahih Bukhari: No. 1682, Narrated by Amr bin Dinar (may Allah be pleased with him):
We asked Ibn 'Umar (may Allah be pleased with him) whether a man who had performed the Tawaf of the Ka'ba but had not performed the Tawaf between As-Safa and Al-Marwa yet, was permitted to have sexual relation with his wife. He replied, "The Prophet (may Allah blessings and peace be upon him) arrived (at Mecca) and circumambulated the Ka'ba seven times and then offered a two Rak'at prayer behind Maqam-lbrahim and then performed the going (Tawaf) between As-Safa and Al-Marwa (seven times) (and verily, in Allah's Apostle you have a good example." And we asked Jabir bin 'Abdullah (the same question) and he replied, "He should not go near her till he has finished the going (Tawaf) between As-Safa and Al-Marwa."
I also wonder when reading following verses from the Qur'an:
Heaven:
The seven heavens and the earth and all that is therein, glorify Him and there is not a thing but glorifies His Praise. But you understand not their glorification. Truly, He is Ever Forbearing, Oft-Forgiving. (Qur'an: 17.44)
See you not how Allah has created the seven heavens one above another, (Qur'an: 71.15)
Hell
"It (Hell) has seven gates, for each of those gates is a (special) class (of sinners) assigned. (Qur'an: 15.44)
If you believe in Allah and His Rasool, just obey. Qur'an and Sunnah are guidelines for muslim. What will happen if there is no guideline? People will do it at their own whim and fancy...mankind need to be guided. Rasool did 7 times, so it is seven times. He is our qudwah so we follow him.