With a primary reason being they can find very little time to incorporate anything other than constant cast healing into their rotation, and the fact that it is just expected of them to tolerate it.
those healers seriously need to get good then

divine seal, synastry, fairy being fairy, simply using cure II or Benefic II instead of cure 1/benefic1 spam, dungeons are so trivial in incoming damage input that my fairy can literally do the healing a lot of the time on my scholar.

i mean no offense but the only differenece between a str tank and a vit tank insofar as damage is concerned is the later can survive longer without being healed. That does not mean they take more damage, and Regen / Aspected Benefic / Fairy will still overwhelmingly handle a huge portion of required healing with proper CD use, and even WITHOUT cd use you wont have to dip out of cleric stance that often even with a str tank.