Why do the Shi'ah build Masjids around the burial sites of Imams?

In Qur'an, we read:

And thus did We make (people) to get knowledge of them (companions of the Kahf) that they might know that Allah's Promise is True and that as for the Hour there is no doubt about it. When they disputed among themselves about their affair and said: Erect a building over them, their Lord best knows them. Those who prevailed over their affair said: We will certainly raise a Masjid over them.

(Qur’an, Surah Kahf(18), Verse 21)

The fellows of the Cave (Kahf) were Believers whom God raised from approximately 300 years of sleep (Qur'an, Surah Kahf, Verse 25).

They were special people whom Allah through them, reminded people regarding His Power to resurrect beings. The people who comprehended this celestial issue, built a Masjid around their burial site so that people may be reminded of Allah's Omnipotence there and worship Allah; it is narrated in Behaar al-Anwaar and … from Imam Sadiq (SBUH) that when Muslims prevailed over Nasaara (christians), the Muslims built a Masjid at the Cave’s (Kahf’s) door.

According to Qur'an, Masjid is the place for worshiping Allah and not for worshiping people buried in it: 

... Masjids, wherein the name of Allah is commemorated in abundant measure ...

(Qur’an, Surah Hajj(22), Verse 40) 

The Masjids around the burial sites of the Infallible Imams (SBUT) are places for worshiping and remembering Allah, and God has given permission for His worship in these places: 

In Houses which Allah has permitted to be exalted and in them, His name may be remembered; in them, He is glorified in the mornings and the evenings.

(Qur’an, Surah Noor(24), Verse 36) 

In addition, the blessed-ones are the Allah-permitted means for seeking and getting close to Allah (Qur’an, Surah Maa’edah(5), Verse 35); we cordially invite our friends to read the articles ”Toward God” and “Seeking the Waseelah” in this site: kindfather.com

As samples in this regard, in the Nahj al-Balaghah of Shi'ah documents, Sahih Bukhari of Sunni documents and many other documents, we observe historic events such as the time when Muslims sought blessings from the drops of water falling from the Prophet Mohammad's (SAWA) hands when washing to pray (Wodu), and in another event, at time of the War of Khaybar, we read that ‘Ali's (SBUH) eyes- which were aching- were healed by the Prophet (SAWA) using the water of his blessed mouth, and many more occasions such as these … The Chosen-ones are blessed by Allah and in their deaths, they are next to God and are considered alive:

Think not of those, who are killed and have given their lives in the cause of Allah, as dead; Nay, they are living, they are provided for, next to their Lord.

(Qur'an, Surah Aale-‘Emraan(3), Verse 169)

The Prophet Mohammad (SAWA) built the Mosque of the Prophet (Masjid-O-Nnabi) in Medina himself and asked to be buried in it. According to Islamic documents, one Rak'at of Salaat in Masjid-O-Nnabi is equivalent to at least one thousand Rak’ats of Salaat else where. (Shi'ah Documents: Kaamel al-Ziyaaraat; Osool al-Kaafi; ...) (Sunni Documents: Sahih and Hajj of Moslem; ...)

The Shi’ah, based on the Majestic Qur'an and the Sunnah of the Prophet Muhammad (SAWA) worship ALLAH AND ONLY ALLAH in the Allah-permitted most blessed places …

Going on pilgrimage of chosen ones- as commanded- is the perfect manifestation of Allah’s obedience and many blessings are promised for it.

May Allah bestow upon us many such opportunities … AAMEEN