It’s called hedging your bet. Yeah, you’re 95% sure yahoo is useless, but if that 5% happens you’ll look like a complete idiot and be locked out.

There was some speculation on Blind that it's a technique to ensure the transaction completes. So, it's a hedge against obstacles during closing.

Yahoo has large and growing customers (example: DuckDuckGo)

What is DuckDuckGo buying from Yahoo? I was under the impression that both search and ads has supplied by Microsoft.

Who does Microsoft partner with for ad monetization? Verizon Media

But still how does that make DDG a Yahoo customer?

DDG was a collection of perl scripts around Yahoo BOSS (Build You Own Search Service), which is now backed by Bing. Nowadays, DDG has vastly outgrown its original serving by adding their most crucial ingredient: Privacy FUD.

That still doesn't really answer the question of how DDG is a Yahoo customer. BOSS is dead, and replaced by an ad program, which DDG doesn't use.

That's true, I was just explaining why one would think DDG is a Yahoo customer.

I thought that DDG was getting its data from Bing... but either way, Yahoo was getting its data from Microsoft.