Why Sankara established Mayawad or Advaita vad Philosophy?

Siva spoke to Parvati as follows:

mayavadam asac-chastram pracchannah baudham ucyate

mayaiva kalpitam devi kalau brahmana-rupina

O Goddess, in the age of Kali I shall descend in the form of a brahmana to spread this Mayavada philosophy which is actually covered Buddhism. (Padma Purana)

 Supreme Lord ordered Siva in this way:

svagamaih kalpitais tvam ca janan mad-vimukhan kuru

mam ca gopaya yena syat srstir esottarottara

Make the general public averse to Me by some imaginary hypothesis from you. Also camouflage me, so that the public will be deluded gradually by desire for material advancement. (Padma Purana)

Also, in the Varaha Purana Lord Visnu instructs Siva saying:

esa moham srjamy asu yo janan mohayisyati

tvam ca rudra maha-baho moha-sastrani karaya

O mighty-armed Siva, please write books filled with lies, and thus bewilder the people.

atathyani vitathyani darsayasva maha-bhuja

prakasam kuru catmanam aprakasam ca mam kuru

O mighty-armed one, please preach a collection of lies. Place yourself in the forefront, and conceal Me.

In this way the Lord ensured that only his true devotees would be able to recognize the pure path of devotion and those of a demoniac mindset would be led astray by this false philosophy.