Here’s the chart that explains why CBS and Viacom want to merge

In 2016, Shari Redstone wanted Viacom and CBS — the media companies her family controls — to merge. In 2017, she changed her mind, and said they were fine on their own. Now she wants them to hook up again.

Last year, Redstone’s argument for keeping the two companies apart was that Viacom, the once-mighty cable programmer that had fallen into disrepair, could improve on its own.

But even if Redstone believed that, it looks like the rest of the media industry won’t wait for Viacom’s turnaround.

A series of proposed mergers, kicked off by AT&T’s planned acquisition of Time Warner, is forcing smaller media companies to look for larger homes. The operating theory: Programmers need to bulk up in order to get leverage with distributors — or find a distributor who just wants to buy them.

And while Viacom and CBS are giant media companies that reach tens of millions of people every night, by the standards of today’s media landscape, they’re comparatively small: Investors value CBS at $23 billion, and Viacom at $14 billion. By comparison, Time Warner is worth some $72 billion, and Disney, which is worth $168 billion, is swallowing a big chunk of 21st Century Fox, which for now is worth $67 billion.

Here’s a visual representation of the market: We’ve grouped distributors and content companies by market cap, and highlighted some of their main lines of business. Note the digital guys on the right side of the chart — many people think Netflix, with its boom streaming business, is spurring some of this consolidation, and we’re still waiting to see if the truly big tech companies like Apple and Amazon enter the market for real.