I would guess simply cost. Air conditioning has a high energy cost, especially if your building isn't air tight, which many old buildings are not. In the UK com

I would guess simply cost. Air conditioning has a high energy cost, especially if your building isn't air tight, which many old buildings are not. In the UK companies can be tight fisted about air conditioning even though they could afford it; an abbey in Hungary may not have enough revenue to pay for it. Having said that I wonder if they also have a damp issue, insects need some degree of moisture if they are eating stuff like paper.