This is the key aspect:

The Duchy of Lancaster’s website states that “proceeds” of bona vacantia go to three registered charities after costs are deducted. However, its accounts suggest only 15% of the £61m it has collected in bona vacantia over the last decade has been donated to charities.

That’s basically fraudulent.

They are within their legal rights but the British taxpayers already do a lot for them through pure goodwill, and they are trespassing on that goodwill.