Because people are better at signalling. Whenever something good happens, there is a person ready to take credit for that, deserved or not.
Markets are good at signalling about individual products or companies (advertising), but not about the concept of "market" per se.
The last point reminded me of speculation from the recent LessWrong article Conspiracy Theories as Agency Fictions:
Before thinking about these points and debating them I strongly recommend you read the full article.