One very important matter that must be noted is that the reasons for the concealment of the graves of Imam Ali (as) and Lady Fatimah (as) differ.
The reason for Imam Ali's (as) grave being concealed was that at that time, ignorant and scurrilous individuals held the hate and enmity of Ali (as) in their hearts; there were chances they would show disrespect to his grave. But as time went on they perished one after another, in addition to the strengthening of the school of thought of the Ahlul-Bayt, and the chances of anything like that happening decreased dramatically. At the same time, since his grave was located in the desert amongst reed beds, the people had no clue where it was even approximately located in order to visit that area and benefit from its blessings. All of this gave rise to the imams informing their sincere companions of its exact location, and later on, as the Shia took root and strengthened, its location was disclosed to all.
As for the reason behind the concealment of Lady Fatimah’s (as) grave which was done by her own command and will, it was a form of protest to the movement that had begun after the prophet’s (pbuh) death regarding the caliphate, and the trampling of rights and the truth. Therefore, until the time when the Muslim ummah doesn’t believe in this truth and don’t renounce the caliphate that took place then that caused many to be deprived of many Islamic secrets and truths, the reason for her grave’s concealment will remain, hence the concealment of her grave.
Another point that must be made is that her grave is a barrier that doesn’t allow the alteration of the history of the advent of Islam and prevents from some claiming that she didn’t have any objection to the circumstances then regarding the caliphate. This issue itself is a sign for those who are thirsty for the truth, guiding them to the shore of salvation and blowing away the dust that covers the truth, leaving no excuses for anyone.
At the same time, although no one knows the exact location of her grave, the approximate area that she is buried has been mentioned and the people can go there in order to benefit spiritually.
Anyway, what was mentioned here were points that are backed by clues and evidence, but doesn’t meant that the reasons for their concealment is limited to such; it is possible for there to be other secrets and reasons that will be discovered and unveiled in the future.
 See: Ibn Abil-Hadid, Sharh Nahjil-Balaghah, vol. 16; Sheikh Abdullah Naser, Mihnatu Fatimah ba’da Wafati Rasulillah (s) (Nusus Tarikhiyyah Min Masadiril-Sunnatil-Mu’tamadah), pp. 197-206.
 According to hadiths, the places where Lady Fatimah (as) might be buried is between the pulpit and altar of the mosque of the prophet (pbuh), her home or the graveyard of Baqi’.