How do Buddhists justify or explain that monks and/or temples amass and use wealth?
One should feel pity for those ignorant monks for they're sowing some very bad seeds for their future's well-being:


  Bhikkhus, there are these five themes that should often be reflected upon by a woman or a man, by a householder or one gone forth. What five? (1) A woman or a man, a householder or one gone forth, should often reflect thus: ‘I am subject to old age; I am not exempt from old age.’ (2) A woman or a man, a householder or one gone forth, should often reflect thus: ‘I am subject to illness; I am not exempt from illness.’ (3) A woman or a man, a householder or one gone forth, should often reflect thus: ‘I am subject to death; I am not exempt from death.’ (4) A woman or a man, a householder or one gone forth, should often reflect thus: ‘I must be parted and separated from everyone and everything dear and agreeable to me.’ (5) A woman or a man, a householder or one gone forth, should often reflect thus: ‘I am the owner of my kamma, the heir of my kamma; I have kamma as my origin, kamma as my relative, kamma as my resort; I will be the heir of whatever kamma, good or bad, that I do.’ ~~ AN 5.57 ~~