Why Beej's Guide to C doesn't use Bing (or DuckDuckGo)

First: an apology for being clickbaity. I love DuckDuckGo. I want to use DDG to search Beej's Guide to C. This really isn't their fault. It's Microsoft's.

See, DDG relies on Bing, and Bing won't index this site for some reason.

So DDG is blind to this content. And so is Bing.

Here's Google's search of the C guide (try searching for "acos"):

And here's DDG's:

(I know I can turn off the Google logo in the search, but I've left it in there just to rub salt in Microsoft's wound.)

I've added a sitemap (which wasn't required), I'm not trying to do any SEO scamming, and I've done all kinds of stuff through Microsoft's webmaster tools to try to fix it, but it always reports:

The inspected URL is known to Bing but has some issues which are preventing indexation. We recommend you to follow Bing Webmaster Guidelines to increase your chances of indexation.

It's worth noting that Bing has no trouble with any of my other guides.

The only thing I can see in Microsoft's documentation that I might be in violation of is their prohibition on sites that are too similar. The landing page for this guide is, indeed, very similar to that of the other guides, but the similarity stops there; the content is completely different. I'm not going to start throwing in random keyboard cat GIFs just to make the landing page different enough to fool Microsoft's filter, if that even is the problem.

Running MS's diagnostic let me know that I was missing the lang attribute in my <html> tag, but that was it. (I've added it, but if Bing restricted sites based on that, 99% of the web would remain unindexed.)

So I contacted them in a last-chance Hail Mary.

They said they'd get back within 10 days. (They put the "10" in bold in their reply to my submission.)

And just 18 days later, I got a reply:

Thank you for your patience!

After further review, it appears that your site https://beej.us/guide/bgc/ did not meet the standards set by Bing the last time it was crawled.

Bing constantly prioritizes the content to be indexed that will drive highest users satisfaction. Please review our Bing Webmaster Guidelines, to better understand criteria for most valuable content.

Maybe it's just not "valuable content". If me spending years writing a book on C and giving it away for free with no ads isn't valuable content to Bing, it just goes to show how much they hate the language. 😜

But if they're not indexing this, you have to wonder what other content they aren't giving you.

Fix your broken algorithm, Microsoft. That way I can stop advertising your best friend, Google. Wouldn't that make you happy?