When Yahoo was founded, Tumblr's most important demographic wasn't even born. This — not profit or monthly active user numbers or corporate image-making — is what explains why Yahoo wants Tumblr.
Yahoo is not the kind of site people have a strong affinity for. As a search engine, or a portal, it's the type of site you choose out of familiarity, or by default. It's the largest homepage of the post-homepage era. As a result, it doesn't seriously overindex in any demographic. Perhaps its most enthusiastic users are old, but they're few, too. The majority of its users are, if anything, apathetic. They're just there.
Tumblr, on the other hand, is the young internet users' service of choice. It's rotten with young people, including a great deal of teens, many of whom use smartphones to check it and make updates (the only way Yahoo is on young people's smartphones now is as a logo in Apple's weather app).
Young people dictate Tumblr's culture, and their interest dictates its future. David Karp, Tumblr's founder, has remained a sort of adult teen avatar, allergic not just to selling out, but to making any money at all.
Karp is known to be capricious and hard to read, which may help explain why early news of Yahoo's interest in Tumblr came as such a surprise. Chris Mohney, Tumblr's editor in chief until an unceremonious and surprising editorial purge in April, tells BuzzFeed over email, "What's to get beyond a giant pile o' cash? Nobody outside of senior management had a clue, far as I know."
Regardless of the management mechanics of the deal, and whether or not Karp will stay on as Tumblr's leader, a Yahoo acquisition would allow him to relinquish the one responsibility he seemed to relish less: the responsibility to keep Tumblr solvent.
To Tumblr's users, Yahoo doesn't just represent an outside force or a threat of advertising. It represents adults, and everything that word connotes: order, boredom, not "getting it." Tumblr's most coveted users aren't afraid of Yahoo because of its turbulent management over the last 10 years, or because of its current leader, or because of what happened to Flickr or Konfabulator or del.icio.us or any number of other beloved services that Yahoo has acquired and let wither on the vine. They're afraid of Yahoo because they don't know what the hell it is, or why it has a billion dollars to burn. They've never seen Yahoo's dot com ads, or heard the Yahoo yodel. To them, and even to many people who used the search engine in the past, Yahoo has been reduced to a disembodied purple logo.
If Yahoo can use this to its advantage — and it's not clear that it can — it will be by staying out of the way. Tumblr users, from here on out, will blame every site change on Yahoo, in the same way that Instagram users assume every new app update came straight from the desk of Zuckerberg. But Instagram users know what Facebook is, and why they don't want Instagram to become more like it.
But Yahoo, despite its long and largely inauspicious history of acquisitions, only has to woo a demographic that's never suffered through one. Yahoo, to young people, is a nearly blank slate. This is its curse, and probably not its salvation. Either way, it's Yahoo's reality.