In case it's not obvious, Taboola hasn't been making money by connecting people to content they want to read, but rather by selling passive tracking data.

If a browser goes to ten sites which have Taboola boxes on them, then Taboola can sell the history of that cookie and its browsing history to a targeting company. If the targeting company has a cookie of its own in the same place as a chumbox then the company is able to map everything Taboola knows to everything they know.

Given the efforts of Apple, Google and Mozilla to choke off this type of tech (third party cookie tracking) it's interesting their valuation is this high. I guess they can still make much of counting anonymous visits and mapping them back to IPs for sale.