It may be due to the region in which those scholars live and therefore which types of thought have influenced the idea of spirituality in that region. The term 'irfan' began to be used under the Safavids, to distinguish it from 'Sufism', or 'tasawwuf', which came to be associated with many spurious groups adopting various practices that had little basis in Islam. If we use the term 'Islamic mysticism', it covers a wide range of spiritual trends which have been incorporated into the field. The type of 'irfan' that may be found in Khorasan would differ from that found in Baghdad. Generally, 'irfan' as understood today, includes the thought and practice of mystics, be they Sunni or Shi'i and be their mysticism influence by Platonism or Neo-Platonism. This view of 'irfan' takes an inclusive approach to spiritual tendencies among mystics.
With regard to 'philosophy' - this term in the Muslim world basically means Platonic-Aritotelian influenced philosophy. There are many other kinds of philosophy also - so the condemnation of philosophy does not mean philosophy per se, but this Greek-influenced trend.
Primarily, both these fields have been disapproved of in narrations attributed to the Imams (as), because both side-line or play down the central pillar of walayah. According to traditional Shi'i narrations, the Imam is the gateway to Allah (swt), the Greatest Sign and the Qutb. Ma'rifah of the Imam = Ma'rifah of God's theophany on earth. There is no greater sign than the Imam (Imam 'Ali (as) says this in Usul al-Kafi).
The are narrations from the Imams that indicate that certain people used to sit in their circles, learn their doctrines, and then go and attribute those doctrines to themselves. This could be one root of the beginnings of Sufism. Hakim Tirmidhi, in his book Sirat al-Awliya' (The Concept of Sainthood) pretty much repackages the Imami concept of walayah, but replaces the Imam with that of the Saint, or Waliyullah (Friend of God). At the same time, he was writing polemical treatises against the Shi'a. Therefore, those who, in time of the Imams, sat in dhikr circles, or passed on the teachings of the Imams, while effectively breaking their allegiance to the Imam and attributing their teachings to themselves, were condemned. Thus, those who say that 'what it matter where these teachings come from? It all leads back to Allah' overlook the fundamental pillar of walayah and loyalty to the Imam. In effect, if you steal someone's teachings, then those teachings are transmitted on a foundation of betrayal. So there is an ethical problem here.
Some argue that the narrations attributed to the Imams that condemn irfan and philosophy are not authentic. This would require more expert investigation to ascertain their status.