That's not quite right. The market is not the economy (although the two tend to share direction most of the time). The S&P 500 is designed to measure the returns of the largest public American companies that are profitable. If it were designed to measure the state of the broader economy, it would need to include a lot of different metrics.
The fact is, the profits are shifting away from the old guard like P&G, GE, ExxonMobil, etc. and towards innovative and disruptive companies that are harvesting the fruits of a cost-lowering of technology and breakthroughs in genetics, new energy, computing, etc. This is why the S&P is becoming less relevant every month. It's happening quickly. The S&P's inaction on Tesla reminds me of the band playing on as the Titanic sank.
A few years back I was a big proponent of individuals harnessing the power of Index funds to build wealth. I can no longer recommend that strategy and I have to assume others are seeing the same things I'm seeing. If there is a mass exodus from passive investing, it will actually be a net negative to own companies listed on the major indexes (and the S&P in particular). Because S&P Index funds would need to be sold off to transfer capital to active managers and this should cause the valuations of companies listed there to decline. This might sound far-fetched, but I don't think we are too far from that point. The S&P is not dynamic enough to remain relevant in a world changing so rapidly.