This was approached some years ago on local news but got no real response from any side.
The real reason for all the hidden art is that councils etc convinced themselves/were convinced that 'saving' art looked good and was a good investment.
As time went on the ability to admit what they had spent and to sell anything without looking desperate or uncultured Philistines meant that they simply hid it away.
The recent odd spates of selling off has been driven by desperate financial straits, increasing Insurance costs and a hope that the political climate is in their favour for once.
The main downside for me is that no-one gets to see it, which would at least be some societal use for the spend and equally the efforts of the artists who are forgotten becuase they are not seen.
[OT: Can the site support UK English 'spel chucking' it really throws you off when in verbose mode and you get US English errors.
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Any excuse when you cannot type