Artists have depended on public support for generations (if not longer) and that support does not artificially prop up its value. In some cases artists and their work can languish for decades until publicly supported exhibitions choose to highlight them. Only then does "the market" value their work, and only sometimes does it do it properly.

And that's not to mention the value art plays in civic life and its contribution to society: markets can frequently fail to properly support artists when society needs them the most (during political strife or civil unrest.)