For property tax exemption, it is often worded as 'place of worship'. This would then include not only 'Kingdom Hall' and 'Assembly Hall' but also synagogue, temple, mosque etc..
WT take additional advantage as they claim printing and administration facilities, warehouse and parking space, housing complexes and individual homes used for Bethel workers and visitors, and other non-worship uses, are also included in the exemption, only because they are owned by a religious organization.
I had previously seen Brooklyn newspaper articles refer to growing public dissatisfaction expressed to city hall regarding WT's tax exemption on the high number of local properties which resulted in area residents paying a disproportionate share of property taxes. I suspect WT were well aware of this and that may have influenced the decision to sell off Brooklyn properties and relocate to rural upstate locations.
Buying the contaminated property might be considered by WT as a means to offset lost property tax revenue complaints as that property might not have otherwise been cleaned-up without local government involvement and expense.