They get a tax REBATE back from the UK Governement (20%) for doing it!
To receive a REBATE, would imply first paying tax. Since WT is a tax exempt charity and a religious organization, I suspect ongoing donations to other charitable organizations is likely one means to maintain tax-exempt charitable status.
It would be interesting to know the other charities WT donates to as well as their backgrounds. One site I read some time ago, suggested WT appoints trusted elders independent from WT, to register and administer charitable organizations, with no traceable link to WT. By donating to those charities, WT is essentially donating to itself. To continue to qualify as a charity, those charities then donate to each other.
A second method for appearing to reduce WT assets was mentioned. When the entire organization, often including individual congregations, purchase supplies and services from specific suppliers required by WT, we would usually expect substantial cost savings would be realized. It seems in WT's case, prices paid are often substantially higher even as the supply companies are often owned by JW's. Are these JW owned suppliers then forced to provide tax exempt donations of any overage to other charities owned at arms length by WT?
I recall a prior thread on this forum where at least one example was detailed, where WT donated a substantial sum to one specific congregation for an unspecified purpose. The congregation as a whole was not aware of any such donation and the donation was not reported in the congregation's financial report. It seems only few congregation elders were aware of the 'donation', deposited to a new separate bank account in the congregation's name, but not to be touched as the funds belong to and are held for WT.
Once funds are paid to a charity, potential creditors including courts of law can no longer claim those funds are WT assets in which to collect a judgement against.
It would be interesting if forum members who are professional accountants, will comment if these techniques would actually work to reduce WT assets, regardless of legalities.